Refer following code:
private void FormMDI_Load(object sender, EventArgs e)
{
Form2 objForm2 = new Form2();
objForm2.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedDialog;
objForm2.ControlBox = false;
objForm2.MdiParent = this;
objForm2.Dock = DockStyle.Fill;
objForm2.Show();
}
Hope this will help you.