In this study, a sequentially coupled thermal-elastoplastic finite element model considering the contact constraints of lap interface is developed to investigate temperature field, residual stress field, and welding deformation of full and partial penetration laser welded lap joints based on ABAQUS software, and the accuracy of numerical results is verified through experimental results. Results show that the high-stress zone of the full penetration welded joint is 30% wider than that of the partial penetration welded joint because the heat input of the former is relatively higher. The transverse residual stress on lower plate lap interface of the partial penetration welded joint is 198 MPa and higher than that of full penetration welded joint because the free expansion constraint of the weld metal in partial penetration plate is stronger than that in the full penetration plate. The difference of transverse deformation between the upper plate surface and the lower plate surface of the partial penetration welded joint is significantly larger than that of the full penetration welded joint, which causes the deformation in the thickness direction of the former to be larger than that of the latter.