在QWidget窗口中添加相关事件resizeEvent()函数并编写相关功能代码： 

void Widget::resizeEvent(QResizeEvent *event)
{

    QSize sz=ui->plainTextEdit->size();
    ui->plainTextEdit->move(5,5);
    ui->pabpic->move(5,sz.height()+5);
    ui->plainTextEdit->resize(this->width()-10,sz.height());
    ui->pabpic->resize(this->width()-10,this->height()-sz.height()-20);
    event->accept();
}

运行效果如下：