Dim byteVal() As Byte
Dim str As String

Redim byteVal(1 To wParam) As Byte '看你从DLL发出的消息，wParam参数应该是字串字节大小
CopyMemory byteVal(1), ByVal lParam, wParam
str = StrConv(byteVal, vbFormUnicode)
'str = StrConv(byteVal, vbUnicode)
'上面两个字符转换随便试一个，我这里没得调试

Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" (ByRef Destination As Any, ByRef Source As Any, ByVal Length As Long)

Public Function WndProc(ByVal hWnd As Long, ByVal uMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long 
    dim a(100-1) as byte, lLen as long, str as string
    If uMsg = 12 Then 
        copymemory a(0), byval wParam, 100
        lLen = instrB(1, a, chr(0)) 'C 标准字符串以 \0 结束
         if lLen <> 0 then '如果发送的字符串没有用 \0 结束（因此没有用lstrcpy而是用copymemory），就认为字符串长 100，否则截短
             redim preserve a(lLen-1)
        end if
        str = strconv(a, vbUnicode)
        MsgBox "收到dll字符串消息,字符串是:(" & str & ")" 
   End If 
   WndProc = CallWindowProc(GetProp(hWnd, OLDWNDPROC), hWnd, uMsg, wParam, lParam) 
End Function