By numerical simulation and combining reaction kinetics and gas transport process, the effects of gas flow rate (NH3 and H2), inlet temperature, pressure and chamber height on the growth rate and gas reaction path of AlN-MOCVD with close-coupled showerhead reactor were studied. It is found that the concentrations of AlN film precursor and nanoparticle precursor determine the growth rate and the gas reaction path. Under the conditions of low Ⅴ/Ⅲ ratio(2 000), high H2 flow rate (12 L/min), high inlet temperature(700 K), low pressure(2 kPa) and low chamber height(5 mm), the reaction is dominated by both the adduct path and the pyrolysis path, and the growth rate is relatively high. On the contrary conditions, the reaction is dominated by the adduct path and the growth rate is rather low. There are different reasons for the effects of the above parameters on the reaction path, such as, the high NH3 flow rate brings the precursor out of the growth zone and the high H2 flow dilutes the reaction precursors in the growing region; the low pressure and low chamber height reduce the particle collision frequency and residence time, and weaken the parasitic response; the inlet temperature causes a change in the temperature gradient.