Abstract: The spring in the reheating main-stop valve actuator weared and fractured after serving for a time. The failure cause was analyzed by micro hardness testing, microstructure examination, macro and micro analysis. The results indicate that the contact and friction between the spring and the safety tube resulted in a white layer, which was hard and brittle and had a large number of micro cracks. Under the effect of shear stress, the micro cracks propagated, leading to the failure of the spring.