Abstract: Addressing the early-stage fatigue failures of the trailer axle as occurring during the testing and running respectively,the cause is analyzed.As a result,the cause is identified as follows.After quenched and tempered,the mechanical properties of the trailer axle is not yet up to the target values as required,and surface roughness of the axle as machined is so poor,which leads to stress concentration at its reducing section to initiate the fatigue crack that further expands,and eventually causes the foresaid early-stage failure.Accordingly,to enhance the fatigue life of the trailer axle,measures as below should be taken:strictly follow the heat treatment process scheme,improving the surface roughness of the axle,and properly conducting raw material inspection,and inter-process inspection and control.