1.将python安装目录中的Scripts文件夹路径加入环境变量，否则pip不能使用。
2.手动下载numpy，用cmd窗口pip工具下载贼慢，容易出错。下载地址：https://files.pythonhosted.org/packages/e9/0f/b1aaf961980d5ea94243f28f91d3f6fc6f3b7e5047a9b8dc037541c2cc11/numpy-1.18.0-cp37-cp37m-win_amd64.whl
3.手动下载opencv模块。下载地址：https://files.pythonhosted.org/packages/74/41/b01f308ca4a22c8c368ed4ee80ef5318efe2f221cd0024a3a0ee9df6a94d/opencv_python-4.1.2.30-cp37-cp37m-win_amd64.whl
4.先在cmd窗口运行命令pip install C:\Users\xxx\Downloads\numpy-1.18.0-cp37-cp37m-win_amd64.whl
5.运行命令pip install C:\Users\xxx\Downloads\opencv_python-4.1.2.30-cp37-cp37m-win_amd64.whl