I found that there are many lines in my web log, my server is fedora linux.
The lines are "221.8.186.158 - - [03/Apr/2006:16:35:26 +0800] "GET log.cpc.sohu.com:90/?pv.png HTTP/1.0" 200 857 "adsence.sogou.com/index.html?pid=mywebcode&ww=200&dc=3&dir=0&num=6&color=1&charset=gb" "Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)"
61.243.176.38 - - [03/Apr/2006:16:36:11 +0800] "CONNECT tcpconn4.tencent.com:443 HTTP/1.1" 400 310 "-" "-""
These lines continue existing in my log, resulting in a huge size within an hour.
Would you suggest me some ways to solve it. Thank you so much.

You can always take the "big stick" approach, and block all access to your server from those IP addresses:
How can you be sure that these are not legitimate accesses to your website?

Try installing "snort" on your server. This is basically a packet sniffer, and will email you daily with a report detailing accesses to you server.

I hope this helps
--Ian

PS: Please do not post the same thread in multiple forums. It will NOT get you a better or faster or more responses.

Thank you so much.
Since I'm new in Linux, How can i install snort??

What distro are you using? Most distros use either rpm or deb packages, so installing programs depends on what you are using...

--ian