The influence of the inlet structure of planetary reactor on gas reaction path and growth rate in AlN-MOCVD was studied by numerical simulation. By varying the reactor inlet mode, inlet number and position of inlet separator, it is found that, for the inverted two-inlet reactor, i.e., group-III below and group-V above, the concentration of Al-containing particles are higher near the front edge of the substrate, especially the concentration of MMAl is about two orders of magnitude than that of the conventional reactor. Thus the reaction is dominated by the pyrolysis path, and the film growth rate is higher. By optimizing the position of the inlet separator for the inverted inlet, better film uniformity is obtained and the growth rate slightly reduced. When the number of reactor inlets increase from two-inlet to three-inlet and five-inlet, the reaction path changes from the pyrolysis-dominated to the pyrolysis and adduct joined action path, the growth rate increases gradually and film uniformity increases significantly.