The work aims to discover the mechanism of shot peening (SP) to change the surface field and surface morphology of 7075-T651 Al-based alloy. Firstly, the finite element models (FEM) of SP involving single projectile and projectiles were set by ANSYS/LS-DYNA respectively to calculate the 200 μm deep stress distribution on materials surface and the surface deformation via different peening times based on the boundary condition of experiment. Then the collision parameters in the model were corrected by experimental results, including meshing density, number of peening times by shot and contact speed, etc. Finally, the calculation of FEM dedicated the surface stress distribution and mechanism of strengthened layer on surface by SP treatment. Through the contrast, the calculation and experimental results of SP simulation model matched with each other. The stress profile from surface to subsurface via FEM agreed with experimented data. The maximum deviation of surface stress was less than 25 MPa, which indicated that the shot peening strength in the model was correct. Furthermore, the deformation ratio of strengthened layer by 6 times of projectile impacts was less than 6% and gradually tended to be stable. This phenomenon was consistent with the hardening situation of the material via the multiple surface coverage in the SP experiment, which indicated the accuracy of the target model and parameters in FEM indirectly. Through the analysis, the FEM of SP can calculate the stress-deformation on materials surface quickly and correctly and play a positive role in exploring the influence rules of SP technology on the characteristics of materials surface.