Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Sub Command1_Click()
Dim hwndCalc As Long
hwndCalc = FindWindow(0&, "计算器")
Print hwndCalc
End Sub
怎么这个每次都是返回0

你没看到FindWindow的第一个参数传递的是什么类型?.
hwndCalc = FindWindow(vbNullString, "计算器")