In order to study the correlation law between the pit foundation morphology and residual stress field and the parameters of shot peening, the main factors affecting the effect of shot peening and their internal correlation were summarized. In the experiment, the pre-mixed water jet shot peening (WJSP) device independently developed by the research group was used to carry out a platform test on 18CrNiMo7–6 carburized steel. The shot peening coverage rate of the sample surface was changed by adjusting the nozzle moving speed and changing the damping, so as to verify the relationship between the coverage rate and the single-pass pit depth and the residual stress field. The effect of shot peening parameters on the diffusion width and angle is studied by analyzing the jet structure and experiment. The relationship of shot peening intensity and residual stress field was verified by changing the parameters of shot peening. The test results show that the coverage rate is the main factor affecting the single pass pit depth. At high coverage rate, material removal is caused by repeated erosion of pellets, resulting in the increase rate of single pass pit depth is much higher than that at low coverage rate. The pressure is the main factor affecting the jet diffusion angle, and the jet diffusion angle reaches its stable value of 3.3° after 12 MPa. The relationship between the nozzle inlet pressure and the diffusion angle is established by regression analysis. The residual stress field is greatly affected by the peening intensity, the depth of the layer where the surface residual stress and the maximum residual stress value are located, and the total residual stress layer is greatly
affected by the pellet diameter. Compared with the large-size pellet, the small-size pellet can introduce a larger surface residual stress, and the maximum residual stress value is greatly affected by the pellet velocity.