Abstract: This article introduces an incident where a 300 MW steam turbine generator experienced a rotor interturn short circuit fault during the start-up process.It combines the analysis of changes in operational parameters after the rotor interturn short circuit,on-site rotor test inspections and evaluations,and inspections of fault points after the rotor is returned for disassembly.The analysis focuses on aspects such as the design structure of the generator rotor end,plastic deformation of rotor windings,and concludes that the rotor end structure fails to meet the operational demands of deep peaking cycles,which is the root cause of the fault.Recommendations are made for improving and optimizing the end structure design,along with preventive measures.