Abstract: Taking Q345 low alloy high strength steel butt joint as research subject, the three-dimensional thermal-metallurgical-mechanical finite element model was established. The temperature field of single-pass welding was numerically simulated by three-dimensional double ellipsoid heat source model considering phase transformation. The heat source model was simplified based on the extracted thermal cycle curve (TCC). The residual stress distribution of single-pass and multi-pass welded butt joints was calculated by three-dimensional double ellipsoid heat source model and the heat source model simplied by TCC, respectively, and test verification was carried out. The results show that TCC of single pass weld obtained by temperature field simulation was in good agreement with the test results, and the relative error was less than 2.34%, verifying the accuracy of the extracted TCC. The residual stress simulation of the joint by the three-dimensional double ellipsoid heat source model and heat source model simplied by TCC were in good agreement with the test results, and the relative errors of longitudinal residual stress of single-pass welded joint were less than 11.38%, 4.34%, respectively, verifying the accuracy of the two simulation methods. Compared with that of the three-dimensional double ellipsoid heat source model, the calculation efficiency of heat source model simplied by TCC was improved by above 32%.