Abstract: To investigate the distribution of residual stress and plastic strain in high-power laser single-pass full penetration welding joints of high-strength steel, the thermo-elastoplastic finite element analysis of laser penetration welding joint of high-strength steel was conducted based on the peak index increasing double cone heat source model. It was found that the temperature field simulated using this heat source model matched well with the actual weld profile, and the maximum error in comparing key parameters was −3.45%. The residual stress of the welded joint were symmetrically distributed from the center to both sides of the weld seam. The stress distribution at the starting and ending points along path L2 fluctuates greatly, which was consistent with the node temperature history curve. The welded joint was subjected to plastic strain in the weld, but no plastic strain occurred in the range far from the weld. The maximum plastic strain peak and peak gradient in the weld along path L1 were equivalent plastic strains. The longitudinal, transverse, and equivalent plastic strain fluctuations at the starting and ending points along path L2 were relatively large. Moreover, the peak value of equivalent plastic strain was the highest, and the gradient of the peak value of transverse plastic strain was the highest, with values of 0.064 and 0.079, respectively.