GaN　thin　films　were　prepared　by　changing　the　growth　condition.　The　epitaxial　layers　were　grown　by　metal-organic　vapor　phase　epitaxy　on　sapphire　(0001)　substrates,　and　were　characterized　by　photoluminescence,　optical　microscope　and　X-ray　double　crystal　diffraction.　In　the　experiment,　we　used　full　width　at　half　maximum　of　X-ray　double　crystal　diffraction　to　detect　the　dislocation　density,　and　found　the　samples　dislocation　density　was　lowest　when　TMGa　flows　at　70　cm3/min.　Using　the　best　value　of　TMGa　flows,　we　grew　the　samples　by　changing　the　growth　temperature.　Photoluminescence　spectra　showed　that　higher　growth　temperature　is　conducive　to　improve　the　optical　properties,　reduce　the　Ga　vacancies　density　in　the　GaN　samples,　and　improve　the　quality　of　GaN　crystal.　Optical　microscope　test　indicated　that　the　increasing　of　the　growth　temperature　will　improve　the　surface　morphology,　it　gives　the　same　conclusion　with　photoluminescence　spectra　test.