I finally solve this
If you have tow form ,form1 as mdi form and form2 as mdi child form
In button to show form2 write
form2.MdiParent=me
form2.formporderstyle=Windows.Forms.FormBorderStyle.None
form2.ControlBox=false
form2.MaximizeBox=false
form2.MinimizeBox=false
form2.showicon=false
form2.text=""
form2.dock=DockStyle.Fill
This work for me ,It should work for you too.