Abstract: In order to investigate the influence of different welding parameters on the residual stress of a flat plate welding joint, based on the ANSYS software, a lot of 3D thermal elastic-plastic finite element models are developed to simulate the transient temperature and the residual stress fields during welding. According to the numerical simulation results, the calculation formula for the half width of a tension zone is modified by considering the effects of various welding parameters, the number of welding beads and heat flux distribution coefficients of the plate. And then, the estimation formula to predict the longitudinal residual stress is fitted as an exponential function using the modified half width of the tension zone. Lastly, several welding joints are fabricated, and the value and law of the welding residual stress are measured with a hole-drilling strain-gages method. The calculated results using the modified estimation formula are compared with those of measured ones and the comparison shows a good agreement, which verified the accuracy of the modified estimation formula for calculating the residual stress.