我覆盖了鼠标滚轮的main方法，但它导致了我上面写的效果。

void MainWindow::wheelEvent( QWheelEvent* event )

通过使用事件筛选器解决。下面的代码提供了按住ctrl按钮进行放大/缩小的功能。

bool MainWindow::eventFilter(QObject *obj, QEvent *event)
    if (event->type() == QEvent::GraphicsSceneWheel)
        ui->GV_image->setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
        double scaleFactor = 1.15;
        bool ok = QApplication::keyboardModifiers() & Qt::ControlModifier;
        if (ok)
            QGraphicsSceneWheelEvent *scrollevent = static_cast<QGraphicsSceneWheelEvent *>(event);
            if (scrollevent->delta() > 0)
                ui->GV_image->scale(scaleFactor, scaleFactor);
                ui->GV_image->scale(1/scaleFactor, 1/scaleFactor);
        event->accept();
        return true;