Abstract: The 05Cr17Ni4Cu4Nb martensitic stainless steel pump shaft of a gas turbine waste heat boiler feed pump cracked during use. The causes of pump shaft cracking were analyzed by means of macro observation, chemical composition analysis, fracture analysis, metallographic examination, mechanical property test and hardness test. The results show that the cracking nature of the pump shaft was a multi-source start-up fatigue propagation crack induced by the surface processing defects of the chromium plating layer, and the microstructure of the pump shaft contained a large amount of high temperature δ ferrite, with the content of δ ferrite up to 50% in local areas, led to a significant decrease in the impact toughness of the material, weakened the bearing capacity of the pump shaft, accelerated the formation and propagation of cracks at the stress concentration part, and finally led to the cracking of the pump shaft.