The paper reports study on the mechanical properties,hardening depth and microscopic structure of riding tractor central transmission axle subjected to different thermal treatments.The test revealed that the torsional and bending strength of the axle could be raised,without change in material or size when the final thermal treatment of the axle was converted from high-frequency induction hardening to medium-frequency induction hardening,with the result that the axle was able to meet the requirements of 20% increase in engine power.