Abstract: Based on SYSWELD software, a method verified the parameters of heat source and heat input of double ellipsoid mode and two principles guiding how to determine the above parameters were put forward. Through taking the above mentioned measures, the trailing problem of molten pool rear in Guassian and double ellipsoid mode had been successfully solved. The experimental results show that the predicted shape and trend fusion line on top surface and cross section are in agreement with the experimental measurements. It provides theoretical basis and basic data for precise modeling and intelligent control of TIG welding process. The reason why so marked difference between the predicted and practical trend fusion line at the rear of the pool exists was analyzed, which could provide a guide for the future research.