我试过下面的代码。我猜你没有意识到新打开的窗体在另一个窗体下面。

private void button1_Click(object sender, EventArgs e)
    {
        Form2 f2 = new Form2();
        f2.Dock = DockStyle.Fill;
        f2.TopLevel = false;
        panel1.Controls.Add(f2);
        f2.Show();
    }

    private void button2_Click(object sender, EventArgs e)
    {
        Form3 f3 = new Form3();
        f3.Dock = DockStyle.Fill;
        f3.TopLevel = false;
        panel1.Controls.Add(f3);
        f3.Show();
    }

Exam
添加以下解决方案代码

f2.BringToFront();

//f2是一个表单变量
像这样

private void button1_Click(object sender, EventArgs e)
    {
        Form2 f2 = new Form2();
        f2.Dock = DockStyle.Fill;
        f2.TopLevel = false;
        panel1.Controls.Add(f2);
        f2.BringToFront();
        f2.Show();
    }

    private void button2_Click(object sender, EventArgs e)
    {
        Form3 f3 = new Form3();
        f3.Dock = DockStyle.Fill;
        f3.TopLevel = false;
        panel1.Controls.Add(f3);
        f3.BringToFront();
        f3.Show();
    }