GaN:Mg　films　have　been　grown　on　sapphire　at　low　temperature　by　metal-organic　chemical　vapor　deposition　(MOCVD),　and　the　properties　of　p-GaN:Mg　films　with　different　CP2Mg　source　fluxes　and　mol　ratios　of　V　and　III　(V/III)　are　studied.　The　results　show　that　the　screw　dislocation　density　is　decreased　under　increasing　V/III　ratio,　and　the　quality　of　p-GaN　crystal　is　improved.　And　when　the　V/III　ratio　is　3800,　the　CP2Mg　flux　is　up　to　170　sccm,　and　the　p-GaN　film,　whose　narrower　full　width　at　half　maximum　(FWHM)　of　(002)　plane　is　232″,　is　obtained.　It　also　shows　that　the　effects　on　decreasing　edge　dislocation　only　by　increasing　V/III　ratio　are　not　obvious.