The work aims to study the effects of shot peening (SP) with different projectile materials on the surface roughness of Al-based alloy. Firstly, the finite element model (FEM) of multiple SP was established by ANSYS/LS-DYNA to impact the Al alloy, and the displacement data of FEM nodes were collected by the Ra discretization calculation formula to calculate simulation roughness value. Then, model parameters were changed to study the effects of different projectile materials on roughness. Finally, according to the experimental roughness and hardness, the influence rule of different projectiles on the surface roughness and hardness was verified. From the comparison, the results of SP simulation model were approximately same as the experimental results. The deviation of calculated roughness value and the experimental value of the ceramic projectile, steel projectile and glass projectile after SP were 4.8%, 7.8% and 4.1%, respectively. It was proved that the simulation model had higher correctness. Furthermore, the hardness value change trend of the samples after SP of different projectiles was consistent with the change trend of roughness value, which reflected the accuracy of FEM indirectly. The comparison of three different shot peening results shows that steel projectiles provide the highest hardness and glass projectiles provide the lowest roughness, while ceramic projectiles provide relatively good hardness and roughness effects.