@TANWEIGUAN 

Please check the following info if Tether failed to log in TP-Link device:

1. Make sure it is the correct login username/password (admin/admin in default settings and this might be changed by yourself; if the TP-Link device is bound to a TP-Link ID, please check it as well). The username/password is the same as your login credentials for the web management page.

2. Make sure the TP-Link device is using the latest firmware.

3. If the TP-Link device is a range extender using a static IP, make sure the IP address is in the same subnet as your router.

4. Reboot the TP-Link device or restart the Tether app.

5. If the username/password is forgotten, please reset the device manually and use the default login credentials (admin/admin).