Protective layers can not fit well with the surfaces of the materials due to the surface roughness of the K24 nickel based alloy is high. So the laser shock processing without coating (LSPwC) is carried out on the K24 alloy and the high cycle fatigue tests are conducted to verify the reinforcement effect. The mechanisms of the residual stress and microstructures to fatigue performances are discussed. The results show that, compared with the untreated specimen, the fatigue strength of the specimen treated by LSPwC is improved by 16% and that after heat preservation is improved by 11%. Under the effects of the compressive residual stress and high density dislocations that induced by LSPwC, the fatigue performances of the specimens are improved. After heat preservation, the majority of compressive residual stress release, the dislocations have great stability, and this is the main cause of the high cycle fatigue performance improvement.