前提

环境搭建

打开designer

选择创建主窗体，拖入一个按钮

保存主窗体UI文件为firstMainWin.ui

将UI文件转化为python文件

# 可以把E:\Python\envs\pyqt5stu\Scripts\pyuic5.exe添加到环境变量中
E:\Python\envs\pyqt5stu\Scripts\pyuic5.exe -o firstMainWin.py firstMainWin.ui

生成的python文件如下

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'firstMainWin.ui'
#
# Created by: PyQt5 UI code generator 5.15.4
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(726, 592)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(490, 110, 93, 28))
        self.pushButton.setObjectName("pushButton")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 726, 26))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "按钮"))

main.py代码如下

import sys
from PyQt5.QtWidgets import QApplication ,QMainWindow
from firstMainWin import *

class MyMainWindow(QMainWindow,Ui_MainWindow):
    def __init__(self,parent=None):
        super(MyMainWindow,self).__init__(parent)
        self.setupUi(self)

if __name__=="__main__":
    app=QApplication(sys.argv)
    myWin=MyMainWindow()
    myWin.show()
    sys.exit(app.exec_())

运行项目即可