Laser shock processing (LSP) is an innovative surface treatment technique. According to the theory of residual stress field formation by laser shock wave, laser overlapping shock processing of LY12CZ aluminium alloy was analyzed. The diagonal shock process is simulated by FEM using LS-DYNA codes, and the residual stress field in different angle of fall and pressure are predicted. The results indicate that the value of residual tension stress can be increased when diagonal shock, and the value of residual compressive stress will be decreased. The simulated results can provide the basis for experimental studying the diagonal laser shock processing and laser facular overlap.