Public Declare Function DwmGetWindowAttribute Lib "dwmapi" (ByVal hwnd As IntPtr, ByVal dwAttribute As Integer, ByRef pvAttribute As RECT, ByVal cbAttribute As Integer) As Integer
Const DWMWA_EXTENDED_FRAME_BOUNDS As Integer = 9

<System.Runtime.InteropServices.DllImport("user32.dll")>
Public Function GetWindowRect(ByVal hWnd As IntPtr, ByRef lpRect As RECT) As Boolean : End Function    

Public Structure RECT
    Public left, top, right, bottom As Integer
End Structure

Public Function GetScalingPercent() As Integer
    Dim rcFrame As RECT
    DwmGetWindowAttribute(Me.Handle, DWMWA_EXTENDED_FRAME_BOUNDS, rcFrame, System.Runtime.InteropServices.Marshal.SizeOf(rcFrame))
    Dim rcWind As RECT
    GetWindowRect(Me.Handle, rcWind)
    Return Int((rcFrame.right - rcFrame.left) / (rcWind.right - rcWind.left) * 100 / 25) * 25
End Function

注意：对于DWMWA_EXTENDED_FRAME_BOUNDS以外的用途，或者对于pvAttribute使用RECT以外的内容的任何情况，此代码段中DwmGetWindowAttribute的签名都是不正确的。
你的窗口也必须显示在你想要获取缩放比例的屏幕上。所以不要在窗体中使用这个。加载事件