本文介绍在Window10操作系统，Python 3.7.3版本安装PyQT5的过程。

1. 在CMD窗口输入命令：

       pip3 PyQt5

     如果下载速度慢，也可以使用命令：

       pip3 PyQt5 -i https://pypi.tuna.tsinghua.edu.cn/simple PyQt5

2. 修改环境变量：

    用户的Path增加：

           C:UsersuserAppDataLocalProgramsPythonPython37Libsite-packagesPyQt5Qt5pluginsplatforms

           C:UsersuserAppDataLocalProgramsPythonPython37Libsite-packagesPyQt5Qt5plugins

     系统的Path增加：

            C:UsersuserAppDataLocalProgramsPythonPython37Libsite-packagesPyQt5Qt5pluginsplatforms

3. 增加用户环境变量：

      QT_PLUGIN_PATH：C:UsersuserAppDataLocalProgramsPythonPython37Libsite-packagesPyQt5Qt5plugins

4. 不修改环境变量，可能会出现如下错误：

this application failed to start because on qt platform plugin could beinitilaied reinstalling the application may fis this problem

5. 测试代码     

import sys
from PyQt5 import QtWidgets, QtCore, QtGui
 
app = QtWidgets.QApplication(sys.argv)
widgetHello = QtWidgets.QWidget()
widgetHello.resize(280, 150)
widgetHello.setWindowTitle("Demo2_1")

LabHello = QtWidgets.QLabel(widgetHello)
LabHello.setText("Hello World, PyQt5")
font = QtGui.QFont()
font.setPointSize(12)
font.setBold(True)
LabHello.setFont(font)
size = LabHello.sizeHint()
LabHello.setGeometry(70, 60, size.width(), size.height())

widgetHello.show()
sys.exit(app.exec_())