Abstract: A 316L stainless steel pump impeller blade broke. The reasons for blade fracture were analyzed using macroscopic observation, chemical composition analysis, scanning electron microscopy analysis, metallographic examination and microhardness testing. The results show that there were obvious pits and scratches on the surface of the impeller blades, and stress concentration occurred at the pits and scratches. Under the action of the working load and the excitation force generated by blade vibration, cracks appeared at the stress concentration and continued to propagate, ultimately led to fatigue fracture of the blades.