Noise is one of the major serious issues for planetary gear trains (PGTs). This noise is regarded as a noise hazard in certain cases such as helicopter cabins where the sound level reaches 100dB. Herein, planet gears of several precisions are combined to investigate the influence of tooth precision on meshing noise of PGT. The meshing noise of PGTs is generated by stiffness coefficient excitation and error excitation forces; however, the stiffness coefficient excitation is assumed to be constant in this paper because a slight error on the tooth surface does not affect the meshing stiffness. It was found that maintaining the same precision for all planet gears is the best. If one of the planet gears has a precision that is significantly different from that of the others, the sound pressure level increases. The deviation for the maximum error among all meshing pairs, should be restricted to no more than 3μm in case of module one spur gear.