Abstract: By studying the projectile velocity problem in the large-scale shot peening simulation, it is found that the velocity of the projectile when it hits the metal surface is inconsistent due to the influence of mutual collision between the projectiles, and the distribution of the projectiles inside and outside the projectile beam is also inconsistent, so the current method of measuring the projectile velocity has certain limitations. To address this phenomenon, the relationship between projectile velocity and Almen strength in the large-scale shot peening simulation problem is studied based on the coupled FEM-DEM model, which provides a certain reference value for the study of the large-scale shot peening simulation problem.