在经过pyuic之后的文件末尾加上这几行代码:

if name == 'main':
from PyQt5.QtWidgets import QApplication, QMainWindow
import sys
app = QApplication(sys.argv)
mainwindow = QMainWindow()
ui = Ui_MainWindow()
ui.setupUi(mainwindow)
mainwindow.show()
sys.exit(app.exec_())

就ok了