Abstract: In the grinding-in test process of a certain type of spiral bevel gear, the position of the meshing contact area was low and there was a slight abnormal vibration phenomenon. The failure causes of carburized spiral bevel gear of 12CrNi3A steel were analyzed by means of macroscopic observation, chemical composition analysis, hardness test, metallographic examination and precision measurement. The results show that during the grinding process of the spiral bevel gear, the grinding amount was too large, resulting in a significant reduction in the depth of the carburized effective hardening layer in the pitch circle, tooth root and tooth groove of the gear, and a reduction in the microhardness of the tooth surface, which in turn induced abnormal noise and vibration during gear meshing. In addition, the tooth profile parameters had errors in the simulation design stage, which also had a certain impact on the abnormal meshing contact area.