The　adsorption　of　benzene　on　Ag(100)　surface　was　studied　by　use　of　the　density　functional　theory　and　periodical　slab　model.　The　adsorption　energy　and　the　geometric　parameters　on　different　adsorption　sites　showed　that　the　hollow　site　was　the　most　favorable　adsorption　site,　followed　by　the　bridge　one,　and　the　top　site　was　the　least　stable　mode.　The　adsorbed　benzene　molecule　was　parallel　to　the　Ag(100)　surface,　and　the　benzene　ring　was　distorted.　The　C-C　bond　was　elongated　in　comparison　with　the　free　benzene　molecule　while　the　variation　of　C-H　bond　length　was　small.　The　C-H　bonds　of　benzene　bent　away　from　the　benzene-ring　and　Ag(100)　surface.　The　calculation　results　showed　that　the　interaction　between　the　Substrate　and　benzene　molecule　was　relatively　strong　chemisorption.　The　detailed　orbital　and　the　charge　population　analysis　was　given,　and　the　calculated　results　were　compared　with　the　experimental　and　theoretical　results.