Xiaomi mix, two Unicom cards, 1, can be switched with 4g card 2, but it cannot be solved with 4g.

If you can't use 4G, you can try to turn it off, turn it on and restart it. If it still doesn't work properly, you can check whether the default setting of mobile phone-mobile network-mobile data options-voice and data view is 3G. If so, you can choose 4G. Because the specific path of each mobile phone model is different, the actual use method of your mobile phone shall prevail. Please check whether the traffic speed limit or traffic upper limit has been reached. If you still can't use 4G, you can't rule out that it doesn't meet the use conditions. At present, China Unicom's 4G network needs to meet the following conditions:

Condition 1: The mobile terminal supports Unicom's 4G network.

Condition 2: The current place of use is within the coverage of Unicom's 4G network.

Condition 3 Use Unicom USIM card.

Condition 4: The 4G Internet access function has been activated (you can send a short message "KT4G" to 100 10 to apply for activation, and the activation will take effect).

If it can't be used if the above conditions are met, you can contact the local manual customer service to find out whether the base station in your location is out of order and follow the instructions.