如果***为任意字符那就可能也有a 或者b
如果***是固定长度就很好取了.举例为三位:
数组中的就是你要的
Dim str As String = "***b123a456a***b*78b9**a*fcasdfas**b"
Dim i As Integer = 0, j As Integer = Len(str) / 4
Dim strA(j) As String
Dim strTmp As String = ""
For i = 1 To j
strA(i - 1) = Left(Mid(str, 1 + (i - 1) * 4, 4), 3)
Next