P-GaN　films　were　grown　by　MOCVD　with　various　flow　rates　of　Mg.　Crystallography　and　electrical　properties　of　these　P-GaN　films　were　characterized　by　Hall　technique　and　double　crystal　X-ray　diffractometry　(DCXRD).　The　relation　between　the　Mg　flow　rate　and　the　property　of　P-GaN　films　was　discussed.　We　found　that　low　flow　rate　of　Mg　led　to　low　hole　concentration　and　poor　electrical　property,　but　high　flow　rate　of　Mg　made　the　situation　even　worse.　As　the　Mg　flow　rate　increases,　the　surface　morphology　and　crystallinity　of　the　films　become　rough　and　worse　due　to　more　micro　defects　generated　by　doping　Mg,　the　activation　rate　of　Mg　decreases,　and　the　self-compensation　effects　is　enhanced.　The　LED　structure　was　grown　using　the　optimum　Mg　flow　rate.　With　20　mA　current　injection,　the　output　power　of　the　LED　(460　nm)　was　6.5　mW,　the　Vf　and　Vr　were　3.3　and　20　V,　respectively.