In order to precisely evaluate the stress concentration factor (SCF) of the welded tubular joints and verify the accuracy of existing methods, a T-joint was taken as the research object to propose a new modeling method. The weld shape data was obtained via 3D laser scanning technology, and a weld model was established through a reverse modeling approach. By importing the reverse-built weld model into the finite element software, a T-joint model containing the reverse weld model was composed. Axial tensile loading test on the T-joints was conducted, and the SCFs were obtained according to the surface stress interpolation method. The SCFs of the T-joint were calculated by using the proposed model, the American Welding Society (AWS) specification weld model, and the model without welds, followed by a comparative analysis between the calculation results with the test data. Results show that the calculation results of the proposed model are the closest to the test data, followed by the AWS specification weld model. However, the model without welds gives a conservative prediction and cannot accurately predict the distribution of SCFs along the weld toe. In the absence of weld shape data, the AWS specification weld model agrees with the test-data distribution to within 25% error. The proposed method can be conveniently extended to the simulation of other types of tubular joints.