In order to improve the fatigue resistance and service life of differential half shaft gear, the cause analysis and process optimization were carried out for the tooth root fracture failure problem of the gear, and through static torsion strength test, reliability test and impact test, it was found that the cause of tooth root fracture failure was stress concentration caused by tooth root folding defects. Then, combining ANSYS stress simulation and metallographic analysis, a die optimization scheme was proposed to keep the parameters of the warm forging die fillet radius consistent with the cold shaping die fillet radius, and the depth of tooth root defects was reduced. Furthermore, the gear structure design was innovated by adopting the measures such as enclosing the large end of the gear, filleting the tooth root and increasing the wall thickness of the gear back cone. The test verification results show that after optimization, the depth of folding defects at the tooth root is within 0.02 mm, which effectively improves the tooth root defects and enhances the tooth root bending strength and fatigue resistance of the half shaft gear.