In my project, There are few forms (form size is small) to be opened, its opened with different locations in main form.
In main Form there is specified label,

How can I determine which form (may be more than one) on top this Specified Label(on Main Form)

try this

   Dim forms As Form() = {Form2, Form3, Form4}
        For Each form In forms
            If (form.Location.X <= Label1.Location.X + Me.Location.X) _
            And (form.Location.Y <= Label1.Location.Y + Me.Location.Y) Then
                If (form.Location.X + form.Size.Width >= Label1.Location.X + Me.Location.X + Label1.Size.Width) _
                And (form.Location.Y + form.Size.Height >= Label1.Location.Y + Me.Location.Y + Label1.Size.Height) Then
                End If
            End If