应该是改变了窗口的RECT信息导致失效。
可以进一步限制，使鼠标不能碰到窗体边界，试试如下代码：
'俩command
Private Declare Sub ClipCursor Lib "user32" (lpRect As Any)
Private Declare Sub GetClientRect Lib "user32" (ByVal hWnd As Long, lpRect As RECT)
Private Declare Sub ClientToScreen Lib "user32" (ByVal hWnd As Long, lpPoint As POINT)
Private Declare Sub OffsetRect Lib "user32" (lpRect As RECT, ByVal x As Long, ByVal y As Long)
Private Type RECT
left As Long
top As Long
right As Long
bottom As Long
End Type
Private Type POINT
x As Long
y As Long
End Type
Private Sub Command1_Click() '限制鼠标
Dim client As RECT
Dim upperleft As POINT
GetClientRect Me.hWnd, client
upperleft.x = client.left
upperleft.y = client.top
ClientToScreen Me.hWnd, upperleft
OffsetRect client, upperleft.x, upperleft.y
ClipCursor client
End Sub
Private Sub Command2_Click() '取消限制
ClipCursor ByVal 0&
End Sub
Private Sub Form_Unload(Cancel As Integer) '释放
ClipCursor ByVal 0&
End Sub
