1、总代码

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import sys
from PyQt5.QtWidgets import QApplication,QWidget
from PyQt5 import QtCore, QtWidgets

class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName("Form")
        Form.resize(320, 240)
        self.textEdit = QtWidgets.QTextEdit(Form)
        self.textEdit.setGeometry(QtCore.QRect(20, 40, 291, 181))
        self.textEdit.setObjectName("textEdit")
        self.pushButton = QtWidgets.QPushButton(Form)
        self.pushButton.setGeometry(QtCore.QRect(210, 20, 56, 17))
        self.pushButton.setObjectName("pushButton")

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

    def retranslateUi(self, Form):
        _translate = QtCore.QCoreApplication.translate
        Form.setWindowTitle(_translate("Form", "Form"))
        self.pushButton.setText(_translate("Form", "开始显示"))

class MyWindow(QWidget, Ui_Form):
    def __init__(self, parent=None):
        super(MyWindow, self).__init__(parent)
        self.setupUi(self)
        self.pushButton.clicked.connect(self.show_text)

    def show_text(self):
        for i in range(1,50):
            text = '第' + str(i) + '次输入内容'
            self.textEdit.append(text)

if __name__ == "__main__":
    # 适配2k等高分辨率屏幕
    QtCore.QCoreApplication.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling)
    app = QApplication(sys.argv)
    myWin = MyWindow()
    myWin.show()
    sys.exit(app.exec_())

2、更多功能

# 获取文本框中的内容
self.textEdit.text()
#设置内容
self.textEdit.setText()
# 清空文本框中的内容就可以通过设置内容为空就行了
self.textEdit.setText("")