Abstract: The 38MnVS non-quenched and tempered steel semi-axle was developed. The effect of cooling rate after hot forging on microstructure and mechanical properties of 38MnVS non-quenched and tempered steel semi-axle was studied and cpmpared with 42CrMo quenched and tempered semi-axle. The main factors affecting the fatigue life of the semi-axle were discussed. The results show that the size of ferrite and pearlite lamellar spacing of 38MnVS non-quenched and tempered steel reduced by force air cooling after hot forging, and the impact toughness increased from 16.8 J after air cooling to 43.7 J after force air cooling. 38MnVS non-quenched and tempered steel had good hardenability. The fatigue life of 38MnVS non-quenched and tempered steel semi-axle was equivalent to that of the 42CrMo quenched and tempered steel semi-axle, and the fatigue life of 38MnVS non-quenched and tempered steel semi-axle could reach more than 300 000 times by reducing the spline modulus, increasing spline root fillet radius and increasing the depth of the hardened layer appropriately that could replace 42CrMo quenched and tempered steel semi-axle.