Abstract: The welding temperature field of Ni-based superalloy little-section rectangular tube is calculated by using non-contact model. After comparing the simulating results with the measuring ones it indicates big errors when applying this model to the temperature field of little section rectangular in welding simulation. By analyzing the relationship between little-section rectangular tube and welding positioner in the view of mechanic and thermal perspectives, the reason for the errors of simulating results is found out. Based on this reason, the contact model is presented. The heat transfer and stress analysis between little-section rectangular tube and welding positioner are simulated by using direct constraints method, and then the laws of the temperature distribution are gotten. The experimental results show that a "T" shaped temperature-field distribution is formed in the vicinity of the weld. After cooling for a period of time, the temperature distribution of the weldments shows that a lower temperature region exists at both ends, and a higher temperature region exists in the middle of the tube. The computed results are in good agreement with the erperimentally measured results.