Public mycon As OleDbConnection = New OleDbConnection(constr)
dim aa as string
aa=""
Dim str1 As String = "insert into luruxinxi(bianhao)values(@ri)"
Dim com1 As OleDbCommand = New OleDbCommand(str1, mycon)
com1.Parameters.Add("@ri", OleDbType.VarChar).Value = aa

这些代码改成：
Public mycon As OleDbConnection = New OleDbConnection(constr)
dim aa as string
Dim str1 As String = "insert into luruxinxi(bianhao)values('')"
Dim com1 As OleDbCommand = New OleDbCommand(str1, mycon)

直接把空值放进去看看行不；
或者
你尝试一下： aa=Null
看看可不可以。。