In this paper, we investigate the effect of growth conditions on the quality of AlN film grown by metal-organic chemical vapor deposition. We test and analyze the influence of different growth conditions, such as nitridation time, growth time of AlN buffer layer and the flow rate of carrier gas, on the lateral grain size of AlN film. It is found that the redution of nitridation time, the increase of growth time of AlN buffer layer, and the reduction of the flow rate of carrier gas can enhance the lateral growth of AlN film and coalescence of islands and increase the lateral grain size of AlN film. So the quality of AlN film is improved.