The root cause of fatigue fracture is that the fatigue cracks of the gear teeth start from the fatigue source of the dangerous section (such as the tooth root) under the repeated action of excessive alternating stress, which makes the stress on the residual section of the gear teeth exceed its limit stress and cause instantaneous fracture. In the origin of fatigue fracture, it is the starting point for the expansion of the shellfish and radiates outwards. The causes are inadequate load estimation, improper material selection, low gear accuracy, thermal cracking, burn grinding, and root stress concentration. Therefore, the dynamic load spectrum of transmission should be fully considered in the design, gear parameters should be optimized, materials and gear accuracy should be correctly selected, and stress concentration factors should be eliminated by fully ensuring machining accuracy.Random fracture is usually caused by material defects, local stress caused by pitting, spalling, or other stress concentration, or by large hard foreign matter falling into the mesh area.