Abstract: The temperature field and welding deformation of 40mm thick Q690D low alloy high strength steel plate multi-layer multi-pass welding were numerically simulated by using Visual-Environment simulation software and SYSWELD as the solver. The results show that the peak temperature during the welding process is 2200-3550 ℃; the residual stress of the welding seam and adjacent areas is relatively large, which is tensile stress. The maximum value of the residual stress is342.95 MPa. The actual welding residual stress was measured by the hole-drilling method, and the result is in good agreement with the simulated result. The welding deformation is mainly angular deformation.