遇到This application failed to start because no Qt platform plugin could be initialized.

在WIN 10 x64下安装PyQt5，找到C:\Users\Administrator\AppData\Local\Programs\Python\Python35\Lib\site-packages\pyqt5_tools\Qt\bin\designer.exe运行，提示This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem。参考了一些文章，但在具体解决方法上，多数描述不准确，没有解决我的问题。后来经自己反复试验，终于解决了。现分享给大家。

要在系统环境变量中增加如下，

具体环境变量名为  ，QT_QPA_PLATFORM_PLUGIN_PATH

变量值为，C:\Users\Administrator\AppData\Local\Programs\Python\Python35\Lib\site-packages\pyqt5_tools\Qt\plugins