The　work　function　modulations　of　AuCl4　-graphene　system　have　been　theoretically　investigated.　The　calculated　results　of　work　function　modulations　are　in　agreement　with　the　recent　experiment　[ACS　Nano,　4(5)　(2010)　2689].　However,　the　theoretical　works　are　lack　for　revealing　the　mechanism　of　the　work　function　modulation　in　AuCl4　-graphene　system.　Our　simulation　reveals　the　work　function　can　be　modulated　by　the　adsorbed　concentration.　It　should　be　originated　from　the　Fermi　level　shifting　and　the　emergence　of　charge　redistribution.　The　behavior　of　charge　redistribution　can　result　in　the　enhancement　of　the　surface　dipole　and　further　the　modulation　of　the　work　function.　(C)　2011　Elsevier　B.V.　All　rights　reserved.