Abstract: In order to compare the steady state operation performance of half speed millions kilowatts generator with different structure, and to provide reference data for the electrical design, comparison data of steady state operation performance calculated by FEM is obtained as to different sub degree in rotor and slot type of stator and rotor. Conclusions are obtained from analysis and comparison that large scale half speed nuclear generator with such structures as unequal section area of conductor in upper and lower slot of stator, larger sub degree in rotor and different slot depth of rotor, can improve the operation performance of generator and potential wave factor. Therefore, such generator structures should be adopted when designing half speed nuclear generator.