After searching through this list I got many threads about squid's encoding support and http/1.1. Finally I got my problems resolved (for reverse proxy), just use the newest Squid 2.7 version and add two config commands. After installed squid-2.7, added two "http11" keywords into the current squid.conf: http_port 80 accel vhost http11 defaultsite=www.mytest.com server_http11 on What're their uses please see the comments on the default squid.conf. Then started squid and tested it, things work fine. Surely the realserver (like Apache) should send out "Vary: Accept-Encoding" header in its encoding responce. I don't know if this way is perfect, but I really got successfully, so I write it to the list. Thanks!
