Cannot discover the MIJIA Smart LED Desk Lamp

This is the official Python demo

Hi, please make sure “Developer mode” is enabled. If there is no “Developer mode” in the settings of MiJia lamp, please try to upgrade to the latest firmware which supports “Developer mode”.

“Developer mode” is enabled,and the firmware is 1.2.9_43
I’ve reset the lamp many times

You don’t need to reset the lamp. could you get the ip address of the lamp, after you get it, you can run the command below:
telnet ‘ip addr’ 55443

If it can be run successfully, the problem maybe with in the demo.

I can control the lamp through telnet
maybe the demo has some problems

It could be caused by some settings of your router. Are you using Openwrt?

No
My router is Tenda F3 and UPnP was enabled