Abstract: Two to five micrometer thick P-Al_xGa_1-xN/GaN layers with 0＜x≤0.4 were grown by low-pressure metal organic chemical Vapour deposition on sapphire（0001）substrates.For Al concentrations 0.2＜x＜0.7 in the Al_xGa_1-xN layers,the orthogonal-design method is employed to optimize the growth parameters of p-typed GaN,such as the Mg flux,growth temperature,and Ⅴ/Ⅲ ratio.It is found that the hole concentration is reduced by excessively high Mg flux,high growth temperature,and great Ⅴ/Ⅲ ratio.The influence of the annealing temperature on the hole concentration and photoluminescence of p-typed GaN is also studied.The optimum annealing temperature is between 680℃and 750℃.