首先来看一下效果：

大概就是这样子，需要注意的是，这里你需要创建一个基类为Widget的界面来绘制时钟，以至于后期你想把这个时钟放到任意一个界面，你只需要在那个界面的ui里面添加一个widget,然后将它提升为这个时钟界面，并设定它的大小。

widget.h文件

#ifndef WIDGET_H
#define WIDGET_H

#include<math.h>
#include<QResizeEvent>
#include<QGroupBox>
#include<QTimer>
#include<QTime>
#include<QPainter>

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
protected:
    void paintEvent(QPaintEvent *event);

private:
    Ui::Widget *ui;
};

#endif // WIDGET_H

widget.cpp文件

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    QTimer *timer = new QTimer(this);  //连接信号与槽
    connect(timer, SIGNAL(timeout()), this, SLOT(update()));
    timer->start(1000);
    //设置窗体名称与大小
    setWindowTitle(tr("Clock"));
    ui->setupUi(this);
    resize(350,350);
}

Widget::~Widget()
{
    delete ui;
}

void Widget::paintEvent(QPaintEvent *event)
{
    static const QPoint hourHand[3] =
    {
        QPoint(5, 14),
        QPoint(-5, 14),
        QPoint(0, -50)
    };
    static const QPoint minuteHand[3] =
    {
        QPoint(5, 14),
        QPoint(-5,14),
        QPoint(0, -70)
    };
    static const QPoint secondHand[3] =
    {
        QPoint(5, 14),
        QPoint(-5, 14),
        QPoint(0, -80)
    };
    static const QPoint line_long[2]=
    {
        QPoint(0,100),
        QPoint(0,80)
    };
    static const QPoint line_short[2]={
        QPoint(0,100),
        QPoint(0,95)
    };
    //绘制的范围
    int side = qMin(width(), height());
    //获取当前的时间
    QTime time = QTime::currentTime();
    //声明用来绘图用的painter
    QPainter painter(this);
    //绘制的图像反锯齿
    painter.setRenderHint(QPainter::Antialiasing);
    //重新定位坐标起始点，把坐标原点放到窗体的*
    painter.translate(width() / 2, height() / 2);
    //在表盘内添加文字（任意）
    //painter.drawText(-75,-120,100,170,Qt::AlignRight,tr("ROLEX"));
    //设定画布的边界
    painter.scale(side / 200.0, side / 200.0);
    //填充边线设为黑色，也可以设置为NoPen
    painter.setPen( Qt::black );
    //画刷颜色设定
    painter.setBrush(Qt::black);
    //保存painter的状态
    painter.save();
    //设置painter的旋转角度
    painter.rotate(30.0 * ((time.hour() + time.minute() / 60.0)));
    //填充时针的区域
    painter.drawConvexPolygon(hourHand, 3);
    painter.restore();
    painter.setPen(Qt::black);
    //12个个刻度循环
    for (int i = 0; i < 12; ++i)
    {
        painter.drawLine(line_long[0],line_long[1]);
        painter.rotate(30.0);
    }
    //绘制分针转角、刻度
    painter.setPen(Qt::black);
    painter.setBrush(Qt::black);
    painter.save();
    painter.rotate(6.0 * (time.minute() + time.second() / 60.0));
    painter.drawConvexPolygon(minuteHand, 3);
    painter.restore();
    painter.setPen(Qt::black);
    for (int j = 0; j < 60; ++j)
    {
        if ((j % 5) != 0)
        painter.drawLine(line_short[0],line_short[1]);
        painter.rotate(6.0);
    }

     //绘制分针转角、刻度
    painter.setPen(Qt::black);
    painter.setBrush(Qt::black);
    painter.save();
    painter.rotate(6.0 * (time.minute() + time.second() / 60.0));
    painter.drawConvexPolygon(minuteHand, 3);
    painter.restore();
    painter.setPen(Qt::black);
    for (int j = 0; j < 60; ++j)
    {
        if ((j % 5) != 0)
        painter.drawLine(line_short[0],line_short[1]);
        painter.rotate(6.0);
    }
   //绘制秒针转角
    painter.setPen(Qt::black);
    painter.setBrush(Qt::black);
    painter.save();
    painter.rotate(6.0*time.second());
    painter.drawConvexPolygon(secondHand,3);
    painter.restore();

}

main.cpp文件

#include "widget.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}