Abstract: In the reliability road test of an automobile, the transverse leaf spring of front axle broke. By means of macro analysis, micro analysis, chemical composition analysis, hardness test and metallographic examination, the fracture causes of the leaf spring were analyzed. The results show that there was a small folding defect on the surface of the leaf spring caused by improper shot peening process, and there was a stress concentration in the folding part, which created condition for fatigue cracks initiation. In reliability road test, the leaf spring was subjected to repeated alternating bending loads, and the cracks continued to expanded, which eventually led to the fatigue fracture of the leaf spring.