The solution is as follows.
1. Check the mobile phone network Settings, check whether the wifi is correctly set;
2. Replace the wifi signal source and check whether there is disconnection caused by insufficient anti-interference ability;
3. Restart the router and follow the router instructions.
4. Configure the router to set the power and channel of wifi to a reasonable range;
5. Replace the router or update the firmware if you can;
6. Reset the network link to ensure that the phone gets the latest network Settings;
7. Check whether the hardware of the phone is faulty, and try to restore the factory Settings;
8. Uninstall the wifi driver and check whether wifi can be used normally.