Laser shock peening (LSP) is a novel surface processing technique for improving the fatigue properties of metal parts, surface roughness is a critical parameter when fatigue strength resistance is concerned. In this paper, a three-dimensional (3D) finite element model was developed in order to assess the surface roughness evolution induced by multiple LSP. A modified finite element analysis (FEA) method was utilized to compute the vertical displacements profiles, discrete data obtained from the numerical simulations were subsequently input to the proposed discretized formula to calculate the surface roughness R_a. The results obtained from the numerical simulations were in good agreement with the experiment data from open literatures, which validates the proposed approach. After the validation of the numerical model, a parametric study was conducted in order to predict the effects of overlap rates, number of impacts, and pulse energy on surface roughness R_a.