The effect of pneumatic shot peening (PSP) on the fatigue properties of K403 turbine blades has been investigated under the high and low cycle combined fatigue (CCF) load with two types of blades: untreated blades and PSP treated blades. It is found that there is a threshold vibration stress which should be 194MPa. The PSP has a positive effect on the CCF life of blades mainly due to the compressive residual stress resulting in the reduction of the number of crack sources and propagation rate when vibration stresses are below the threshold vibration stress. However, the PSP treatment has no or negative effect when vibration stresses are above the threshold value. The compressive residual stress is released along with the microstructure changes of K403. Meanwhile, the microstructure changes, reflected in the precipitation of the lamellar MC carbides and σ phases, can accelerate the process of crack initiation and propagation.