The　first-principles　calculations　were　performed　to　investigate　the　stability,　band　structure,　density　of　states　and　redox　potential　of　Al-,　Ga-,　and　In-doped　monoclinic　BiVO4　(mBiVO4).　The　calculated　formation　energies　show　that　Al-doped　mBiVO4　inducing　an　O　vacancy　is　energetically　favorable　with　a　smaller　defect　formation　value.　With　the　incorporation　of　Al,　Ga,　and　In,　the　band　gap　of　the　doped　systems　will　be　narrowed　in　the　order　of　Al-doped　<　Ga-doped　<　In-doped　mBiVO4,　which　is　beneficial　for　the　response　to　the　visible　light.　And　the　substitution　of　an　Al　or　Ga　for　a　V　atom　will　significantly　enhance　the　reducibility　of　mBiVO4,　improving　the　efficiency　of　H2　evolution　from　H2O.　Our　results　show　that　the　photocatalytic　activity　of　mBiVO4　can　be　modulated　by　substitutional　doping　of　Al,　Ga,　and　In.