Private Sub MSComm1_OnComm()
    Dim BytReceived() As Byte
    Dim strBuff As Variant
   
    Select Case Case 2
        MSComm1.InputLen = 0
        strBuff = MSComm1.Input
        BytReceived() = strBuff
        Dim i As Long
        For i = 0 To UBound(BytReceived)
           Debug.Print BytReceived(i)
        Next
        If i <= 2 Then
        Text2 = BytReceived(0)
        BytReceived(0) = 0
        Else
        tongyi = BytReceived(0)
        BytReceived(0) = 0
        fandui = BytReceived(2)
        BytReceived(2) = 0
        qiquan = BytReceived(4)
        BytReceived(4) = 0
        End If
    End Select

我这段代码那里有问题   为什么运行时经常出现 错误9，“下标越界”   调试时总指在qiquan = BytReceived(4)这一行

UBound(BytReceived) 是多少？

BytReceived下标<4

什么意思啊！！！

你开始定义数组就考虑上标最大值（比如为4），可定义为：
Dim BytReceived(4)
你也可以如果在你不知开始定义了多大上标的情况下，重新定义为你需要的最大上标，如下：
ReDim Preserve BytReceived(4)
你不妨试试。