Abstract: The condensate pump shaft in a gas turbine plant fractured during runtime. The fracture reasons of the pump shaft were analyzed by means of macro and micro morphology analysis of fracture, chemical compositions analysis, metallographic test, mechanical property test and so on. The results show that improper heat treatment led to the existence of Widmanstatten structure and obvious zonal segregation in the microstructure of the pump shaft, which made its fatigue resistance decline. In addition, the pump shaft was subjected to continuous alternating stress during runtime, which led to premature fatigue fracture of the pump shaft in the stress concentration keyway position.