What kind of slot SIM Best to use for the Internet in two-simony Xiaomi: full guide 2026

Xiaomi’s dual-sim smartphones have long been the standard for users who need to differentiate between work and personal calls or use carrier rates, but when choosing a mobile internet slot, many face a dilemma: Which of the two slots will provide a more stable and faster connection? The answer is not as obvious as it seems - it depends on the phone model, support networks. 4G/5G, modem configuration and even firmware.

In this article, we will analyze the technical features of the distribution of Internet traffic in Xiaomi, analyze the results of speed tests on popular models (from Redmi Note 12 to Xiaomi 14 Ultra), and give clear recommendations for setting up. SIM1 not always better SIM2, How to check the priority of slots in your model, and what to do if the Internet speed drops when the active second number.

Spoiler: 90% of the time the difference between slots is minimal, but there are critical exceptions for models with hybrid slots (e.g., the Spots, POCO X5 Pro where slot selection directly affects support 5G. We will also reveal a little-known trick with forced priority switching through an engineering menu – this will help if the phone “stubbornly” clings to a slow network.

Before you go to the settings, make sure that the problem is not in the tariff or coverage of the operator.

1. Technical differences between SIM1 and SIM2 Xiaomi: Myths and Reality

Many users believe that the slot SIM1 It's always faster because he's the "head" -- and that misconception goes back to the era. 3G-In modern Xiaomi (starting with the Snapdragon 600 and MediaTek Helio G series), both slots are connected to the same modem, and their performance is theoretically identical:

First, hybrid slots (where the second slot is paired with a memory card) can limit speed, such as the Redmi Note 11 Pro.+ when used SIM2 + MicroSD maximum speed 4G limited Cat.12 instead Cat.15 into SIM1. Other models (such as Xiaomi) 12T Pros support 5G only SIM1 — This is specified in the specifications of the Snapdragon 8 chipset+ Gen 1.

Third, firmware. MIUI It can give priority to slots based on activity. SIM2, The system can dynamically reduce the priority of the Internet for the SIM1, This is confirmed by the logs from ##4636## (engineering menu).

• 🔧 SIM1 — It usually has a direct connection to the antenna, less often loses the signal in motion.
• 📶 SIM2 — may be faster in low-course areas if the operator uses frequency aggregation (e.g., MTS with Band 3) + Band 7).
• ⚡ Hybrid slot – speed drops by 10-30% while using SIM2 + microSD.

To check which slot in your model is a “priority” look at the documentation on the official Xiaomi website (Section Specifications). → Network & Connectivity, for example, for POCO F5 indicated: «5G: n1/n3/n5/n7/n8/n20/n28/n38/n40/n41/n77/n78 (SIM1 only)” That means that 5G It will only work in the first slot, and the second is limited. 4G.

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If you use 5G, But the phone doesn't catch the network, try repositioning it. SIM-Slot 1 card, even if previously 4G worked in both slots.

2. How to check the Internet speed in each slot: step-by-step instructions

Before you make a decision, test both slots in real conditions.

1. Two. SIM-Cards of the same operator (ideally - with the same rates).
2. Speedtest by Ookla or nPerf.
3. A stable place with good coverage (such as at home or in the office).

The test algorithm:

1. Put the first one in. SIM into SIM1, second-in SIM2.
2. Activate the mobile Internet only on SIM1 (disconnect the data on SIM2 customized).
3. Run 3 tests of speed in a row, record the average result.
4. Repeat steps 2-3 for SIM2.
5. Compare the results: a difference of more than 20% indicates a problem with one of the slots.

Turn on the aircraft mode and leave only the test SIM|Turn off Wi-Fi and VPN|Testing at the same time of day|Use the same operator's server in Speedtest|Repeat tests in different locations (house, street, office)-->

Example of results for Xiaomi 13 Lite (Tele2 operator, Moscow):

So you can see there's a difference, but it's not critical. 10C With a hybrid slot, the results can vary by 2-3 times! SIM2 more often communication is cut off when moving, this may be due to a weak antenna or interference from the memory card.

3.When Slot Choice Is Critical: 5G, VoLTE and Hybrid Configurations

There are situations when the choice of slot determines not only the speed, but also the functionality:

🔹 5G-As mentioned earlier, many Xiaomi models support the 5G only SIM1. It's about:

• Xiaomi 12/12 Pro (Snapdragon 8 Gen 1)
• POCO F4 GT
• Redmi K50 Pro

If you use 5G, You have no choice – the Internet must be activated in the first slot.

🔹 VoLTE and ViLTE: Voice calls 4G (VoLTEs can conflict with mobile internet if both are activated on the same SIM. So in this case, it's better to spread voice and data across different slots:

• SIM1 — voice (VoLTE) + SMS
• SIM2 — mobile

This will solve the problem of communication interruptions during conversations.

🔹 Hybrid Slots: If your Xiaomi has a slot SIM2 + microSD, remember:

• 📉 Internet speed in SIM2 It can drop by 15-40% with a memory card installed.
• 🛑 Some models (e.g. Redmi) 9A) shut down SIM2, if a microSD is inserted.

🔹 Double activity (DSDA): Technology that allows the use of two SIM-map-mode 4G Supported in flagships (Xiaomi 13 Ultra, Mix Fold 3) in these models, there is no difference between slots, but battery consumption increases by 10-15%.

⚠️ Note: If you use Xiaomi with MediaTek Dimensity (e.g, POCO X5 Pro 5G), Check the modem settings, some firmware when activated. 5G on SIM1 slot SIM2 automatically switched 2G!

4. How to forcefully change the slot priority (for power users)

If tests show that one of the slots is performing worse, but you can’t change it. SIM-Cards can be assigned in places (for example, due to the linking of the number to banking services), you can manually set the priority through the engineering menu:

Instructions:

1. Open the Phone app and enter the code: ##4636##.
2. Go to the Information (or Phone Information) section.
3. Scroll down to the Set preferred network type block.
4. Choose a slot (SIM1 or SIM2) and set the desired network type (e.g, LTE only NR/LTE for 5G).
5. Save the settings and restart the phone.

For MediaTek, use the code ##36446337## (Engineering Mode) and then go to Connectivity. → SIM and manually prioritize.

Warning: Incorrect settings can lead to loss of network or inability to make calls. If after the changes, the phone stopped catching the network, reset the modem settings:

1. Go to Settings. → SIM-maps and mobile networks.
2. Select Network Settings Reset (or Reset Network Settings).

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Changing the slot priority through the engineering menu is a temporary solution. MIUI settings may reset.

5. Internet optimization: additional settings for maximum speed

Selecting a slot is only part of the solution. To achieve maximum speed, follow these steps:

• 📡 APN-Settings: Make sure that the access point settings (APN) For MTS it is Internet.mts.ru, for Beeline - Internet.beeline.ru. APN may limit the speed to 3G!
• 🔄 Network mode: In settings SIM-maps (Settings) → SIM-maps and mobile networks → [choose SIM] → Type of network select 4G (preferably 5G (if supported) Automatic mode (2G/3G/4G) It can get stuck on slow networks.
• 🛡️ Turn off traffic savings: C MIUI There is a function of saving data (Settings) → Connections and sharing → Traffic savings, which limits background activity, which you have to turn off for speed tests.
• 📱 Update the firmware: In new versions MIUI They often optimize the modem. MIUI 14 for Xiaomi 13 improved support for frequency aggregation in the SIM2.

Hidden settings for advanced users:

If your Xiaomi supports carrier aggregation (CA), You can manually turn on extra frequencies:

1. Install the NetMonster or Network Cell Info Lite app.
2. Check what band frequencies are available in your location.
3. Using the engineering menu (#4636##) in Band Selection, activate all supported frequencies for your operator.

For example, for MegaFon in Moscow, it is useful to include:

Band 3 (1800 MHz) + Band 7 (2600 MHz) + Band 20 (800 MHz)

This can increase speed by 30-50% by using multiple frequencies at the same time.

⚠️ Warning: Activating unsupported frequencies can cause the modem to overheat and consume more battery. If the phone gets hot, return settings to factory settings.

Frequent problems and their solutions

Even after you've set it up properly, you can have a lot of problems.

🔴 The problem is that the Internet only works in SIM1, SIM2 no.

🔹 Decision:

• Check if the slot is hybrid (if so, get the memory card).
• Update the firmware (in) MIUI 12.5 was an error with SIM2 on some models).
• Try another one. SIM-The map may be the problem in the map itself.

🔴 Problem: Speed in SIM2 falls sharply when an active call is made SIM1.

🔹 Decision:

• Turn off VoLTE for SIM1 (Settings → SIM-map → Challenges → VoLTE).
• Use it. SIM2 just for data, and SIM1 — call-only.

🔴 Problem: 5G It does not work in any slot, although the operator maintains the network.

🔹 Decision:

• Make sure your tariff includes 5G (Tele2 and Iota don't always default).
• Check the list of supported frequencies 5G for your model on 4pda.ru.
• Reset network settings (Settings) → The phone. → Resetting settings → Resetting Wi-Fi, Mobile Network and Bluetooth).

🔴 Problem: After the update MIUI The Internet has stopped working SIM2.

🔹 Decision:

• Reverse to the previous version of the firmware (through MIUI bootloader).
• Manual adjustment of settings APN (Sometimes an update will reset them).
• Address in support of Xiaomi with logs (#4636## → Log collection).

7 Model recommendations: which slot is better for the popular Xiaomi

We tested some popular models and made a table of recommendations, so you can focus on it if you don't want to do it yourself.

For flagship models (Xiaomi 14 Ultra, Mix Fold 3) there is no difference between slots - you can choose any. A2+, POCO M5) give priority SIM1, so SIM2 It often has a simplified antenna.

FAQ: Answers to Frequent Questions