关键代码：

    # 设置窗口图标
    icon = QtGui.QIcon()
    icon.addPixmap(QtGui.QPixmap("logo.ico"), QtGui.QIcon.Normal, QtGui.QIcon.Off)
    mainWindow.setWindowIcon(icon)

 

完整测试：

左上角可以看到小图标，任务栏图标需要打包成exe才能看到

import sys

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(480, 318)

        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.gridLayout = QtWidgets.QGridLayout(self.centralwidget)
        self.gridLayout.setObjectName("gridLayout")
        self.textBrowser = QtWidgets.QTextBrowser(self.centralwidget)
        self.textBrowser.setObjectName("textBrowser")
        self.gridLayout.addWidget(self.textBrowser, 1, 0, 1, 1)
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setObjectName("pushButton")
        self.gridLayout.addWidget(self.pushButton, 2, 6, 1, 1)
        self.lineEdit = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit.setObjectName("lineEdit")
        self.gridLayout.addWidget(self.lineEdit, 2, 0, 1, 1)
        self.verticalLayout = QtWidgets.QVBoxLayout()
        self.verticalLayout.setObjectName("verticalLayout")
        spacerItem = QtWidgets.QSpacerItem(20, 30, QtWidgets.QSizePolicy.Minimum, QtWidgets.QSizePolicy.Expanding)
        self.verticalLayout.addItem(spacerItem)
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setIndent(0)
        self.label.setOpenExternalLinks(False)
        self.label.setObjectName("label")
        self.verticalLayout.addWidget(self.label)
        spacerItem1 = QtWidgets.QSpacerItem(20, 20, QtWidgets.QSizePolicy.Minimum, QtWidgets.QSizePolicy.Expanding)
        self.verticalLayout.addItem(spacerItem1)
        self.gridLayout.addLayout(self.verticalLayout, 1, 6, 1, 1)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 480, 18))
        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", "发送"))
        self.pushButton.setShortcut('enter')
        self.label.setText(_translate("MainWindow", "小明"))
if __name__ == '__main__':
    # QtCore.QTextCodec.setCodecForCStrings(QtCore.QTextCodec.codecForName("utf-8"))

    app = QtWidgets.QApplication(sys.argv)
    mainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()  # 窗口类
    ui.setupUi(mainWindow)

    # 设置窗口图标
    icon = QtGui.QIcon()
    icon.addPixmap(QtGui.QPixmap("logo.ico"), QtGui.QIcon.Normal, QtGui.QIcon.Off)
    mainWindow.setWindowIcon(icon)

    mainWindow.show()

    sys.exit(app.exec_())

    pass
pass