The work aims to simulate improvement of residual stress field of welded joint by establishing random shot peening (SP) model. Firstly, the model of Q235B welded joint was established, and the residual stress of the welded joint was calculated by indirect coupling method. Then, the residual stress was introduced into the SP model of the welded joint as the initial condition to evaluate the influence law of shot diameter d, shot velocity v, shot impact angle θ and shot mass flow rate rm on the residual stress field of the welded joint. Finally, the improvement of residual stress field of welded joint after SP was analyzed. The results show that the transverse residual stress σx and the longitudinal residual stress σz of the weld seam can reach 227 MPa and 196 MPa as welded, respectively. Adjusting SP parameters can eliminate tensile residual stress and introduce compressive residual stress. In this simulation d=1 mm、θ=60°、v=60 m/s、rm=9 kg/min are the optimal SP parameters. For σx and σz, the corresponding surface compressive residual stress can reach -246 MPa and -275 MPa, the corresponding maximum compressive residual stress are -306 MPa and -310 MPa, the corresponding depths of the maximum compressive residual stress are 0.24 mm and 0.27 mm, and the corresponding depths of the compressive residual stress layer are 0.78 mm and 0.66 mm. Whether σx or σz, the depth of the maximum compressive residual stress and the depth of the compressive residual stress layer significantly increase with the increase of d and θ,and increasing v can significantly increase the maximum compressive residual stress, the depth of the maximum compressive residual stress and the depth of the compressive residual stress layer. So SP can improve residual stress field of welded joint efficiently.