Due to the significant fluctuation and the real-time measurement difficulty of residual stress, a finite element model of laser shock peening (LSP) on residual stress field of Al alloy welding has been developed in ABAQUS. The residual stress fields of 7075-T6 Al alloy welding are computed and compared before and after LSP, and special attentions are paid to the effects of LSP on residual stress field of 7075-T6 Al alloy welding. Subsequently, the processing parameters of LSP on Al alloy welding are also optimized. Results show that LSP causes the residual stress evolution from tensile residual stress to high-level compressive residual stress on the Al alloy surface. Residual stress distributions can be clearly improved by optimizing the processing parameters (including laser pulse energy, spot size and overlapping rate). When the overlapping rate is between 50% and 70%, residual stress tends to a more uniform residual stress field, which can effectively eliminate “residual stress hole”.