FORM1为主窗体，FROM2为子窗体，FROM2中需要调用FROM1中的DATATIMPICKER1的值

首先你将DATATIMPICKER1的modifiers属性设为public

在form1窗体中

  private void button2_Click(object sender, EventArgs e)
        {
           
            FROM2  f2 = new FROM2(this);
            f2.Show();
        }


在FROM2添加一个构造函数

  public FROM2  ()

        {

            InitializeComponent();

        }

        public FORM1  f1;

        public FROM2(FORM1 fm)

        {

            InitializeComponent();

            f1 = fm;

        }



        private void button1_Click(object sender, EventArgs e)

        {

            MessageBox.Show(f1.dateTimePicker1.Value.ToString());

        }