产生此效果
 
 Public Class Form1
    ' Create a new form.
    Dim mdiChildForm As New Form
    Dim mdiChildForm1 As New Form
    Dim mdiChildForm2 As New Form
 
 
 
    Private Sub Form1_Load(ByVal sender As Object, _
        ByVal e As System.EventArgs) Handles MyBase.Load
 
        ' Set the IsMdiContainer property to true.
        IsMdiContainer = True
 
        ' Set the child form's MdiParent property to
        ' the current form.
        mdiChildForm.MdiParent = Me
        mdiChildForm1.MdiParent = Me
        mdiChildForm2.MdiParent = Me
 
        mdiChildForm.Show()
        mdiChildForm1.Show()
        mdiChildForm2.Show()
        mdiChildForm.Text = 1
        mdiChildForm1.Text = 2
        mdiChildForm2.Text = 3
    End Sub
 
End Class