only thing he need to modify is put the txd & rxd together in pc com port side

You mean a loopback on pin 2 and 3 of PC com port?

Loop back is not a solution for debugging, it will not show any errors in setting port parameters like baud rate, no of bits etc.

In my opinion, what he needs is to rectify his 8052 first using a standard terminal program and then debug his VB code.