1.首先上效果：

2.主要思路

2.1核心

显示视频和显示图片一样需要新建一个QLabel来显示，然后opencv格式的图片不能直接显示，需要用下面代码转换一下

        show = cv2.cvtColor(show, cv2.COLOR_BGR2RGB)
        showImage = QtGui.QImage(show.data, show.shape[1], show.shape[0], QtGui.QImage.Format_RGB888)
        self.label_show_camera.setPixmap(QtGui.QPixmap.fromImage(showImage))

2.2需要设置一个定时器，实时的刷新界面

具体代码见下面：

import sys
import os
import cv2

from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from PyQt5.QtGui import QPalette, QBrush, QPixmap


class Ui_MainWindow(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(Ui_MainWindow, self).__init__(parent)

        self.timer_camera = QtCore.QTimer()  # 初始化定时器
        self.cap = cv2.VideoCapture()  # 初始化摄像头
        self.CAM_NUM = 0
        self.set_ui()
        self.slot_init()
        self.__flag_work = 0
        self.x = 0
        self.count = 0

    def set_ui(self):
        self.__layout_main = QtWidgets.QHBoxLayout()  # 采用QHBoxLayout类，按照从左到右的顺序来添加控件
        self.__layout_fun_button = QtWidgets.QHBoxLayout()
        self.__layout_data_show = QtWidgets.QVBoxLayout()  # QVBoxLayout类垂直地摆放小部件

        self.button_open_camera = QtWidgets.QPushButton(u'打开相机')
        self.button_close = QtWidgets.QPushButton(u'退出')

        # button颜色修改
        button_color = [self.button_open_camera, self.button_close]
        for i in range(2):
            button_color[i].setStyleSheet("QPushButton{color:black}"
                                           "QPushButton:hover{color:red}"
                                           "QPushButton{background-color:rgb(78,255,255)}"
                                           "QpushButton{border:2px}"
                                           "QPushButton{border_radius:10px}"
                                           "QPushButton{padding:2px 4px}")

        self.button_open_camera.setMinimumHeight(50)
        self.button_close.setMinimumHeight(50)

        # move()方法是移动窗口在屏幕上的位置到x = 500，y = 500的位置上
        self.move(500, 500)

        # 信息显示
        self.label_show_camera = QtWidgets.QLabel()
        self.label_move = QtWidgets.QLabel()
        self.label_move.setFixedSize(100, 100)

        self.label_show_camera.setFixedSize(641, 481)
        self.label_show_camera.setAutoFillBackground(False)

        self.__layout_fun_button.addWidget(self.button_open_camera)
        self.__layout_fun_button.addWidget(self.button_close)
        self.__layout_fun_button.addWidget(self.label_move)

        self.__layout_main.addLayout(self.__layout_fun_button)
        self.__layout_main.addWidget(self.label_show_camera)

        self.setLayout(self.__layout_main)
        self.label_move.raise_()
        self.setWindowTitle(u'摄像头')

        '''
        # 设置背景颜色
        palette1 = QPalette()
        palette1.setBrush(self.backgroundRole(),QBrush(QPixmap('background.jpg')))
        self.setPalette(palette1)
        '''

    def slot_init(self):  # 建立通信连接
        self.button_open_camera.clicked.connect(self.button_open_camera_click)
        self.timer_camera.timeout.connect(self.show_camera)
        self.button_close.clicked.connect(self.close)

    def button_open_camera_click(self):
        if self.timer_camera.isActive() == False:
            flag = self.cap.open(self.CAM_NUM)
            if flag == False:
                msg = QtWidgets.QMessageBox.Warning(self, u'Warning', u'请检测相机与电脑是否连接正确',
                                                    buttons=QtWidgets.QMessageBox.Ok,
                                                    defaultButton=QtWidgets.QMessageBox.Ok)
                # if msg==QtGui.QMessageBox.Cancel:
                #                     pass
            else:
                self.timer_camera.start(30)
                self.button_open_camera.setText(u'关闭相机')
        else:
            self.timer_camera.stop()
            self.cap.release()
            self.label_show_camera.clear()
            self.button_open_camera.setText(u'打开相机')

    def show_camera(self):
        flag, self.image = self.cap.read()
        show = cv2.resize(self.image, (640, 480))
        show = cv2.cvtColor(show, cv2.COLOR_BGR2RGB)
        showImage = QtGui.QImage(show.data, show.shape[1], show.shape[0], QtGui.QImage.Format_RGB888)
        self.label_show_camera.setPixmap(QtGui.QPixmap.fromImage(showImage))

    def closeEvent(self, event):
        ok = QtWidgets.QPushButton()
        cancel = QtWidgets.QPushButton()
        msg = QtWidgets.QMessageBox(QtWidgets.QMessageBox.Warning, u'关闭', u'是否关闭！')
        msg.addButton(ok, QtWidgets.QMessageBox.ActionRole)
        msg.addButton(cancel, QtWidgets.QMessageBox.RejectRole)
        ok.setText(u'确定')
        cancel.setText(u'取消')
        if msg.exec_() == QtWidgets.QMessageBox.RejectRole:
            event.ignore()
        else:
            if self.cap.isOpened():
                self.cap.release()
            if self.timer_camera.isActive():
                self.timer_camera.stop()
            event.accept()


if __name__ == '__main__':
    App = QApplication(sys.argv)
    win = Ui_MainWindow()
    win.show()
    sys.exit(App.exec_())