import sys
from PyQt5 import QtWidgets

class Center(QtWidgets.QWidget):
    def __init__(self, parent=None):
        QtWidgets.QWidget.__init__(self,parent)
        self.setWindowTitle("窗口置中程序")
        self.resize(250, 150)
        self.center()

    def center(self):
        screen = QtWidgets.QDesktopWidget().screenGeometry()
        size = self.geometry()
        self.move((screen.width() - size.width())/2, (screen.height() - size.height())/2)

app = QtWidgets.QApplication(sys.argv)
center = Center()
center.show()
sys.exit(app.exec_())