If I want to make more clients to connect to me，can I broadcast udp pong message with my own address within the message making more client know my address？

Thanks~

Look, As far as I know* ,
Peers won't forward any routed packet (PONG, QUIERY HIT,..) unless they forwarded a broadcast packet first before, PING in your case.

* -
GNUtella protocol is quite different now, new techniques are used now in order to improve the protocol performances as pong caching, "leafs - ultrapeers" architecture, etc.

wait for other replies.