thanks to all experts above,your advise and report is helping!
i've contacted host owner,there truely is expliot on my site,and removed some harmful code,but still,we failed to find out where virus comes from,i didt make any special move on this site,system and plugings is updated...really weired...
and after exploit been removed,i used online checking tool test my site,and i got a safe report,but after about 2 hours,when i test again,these virus comes back!but again 1 hour past,until now,virus seems vanished....did i deal with some kind of ghost???