Abstract: The tension spring of a rice transplanter fractured during operation. The fracture causes of the tension spring were analyzed by means of macro observation, chemical composition analysis, mechanical property test, fracture analysis, energy spectrum analysis, metallographic examination and non-metallic inclusion detection. The results show that the fracture property of the tension spring was fatigue fracture. Improper heat treatment process was the root cause of fatigue fracture of the tension spring. After cold drawing, the tension spring structure formed by cold rolling directly was fibrous structure. The fatigue resistance of the structure was too weak, resulted in fatigue fracture after nearly 100 reciprocating cycles of the tension spring.