Abstract: The mathematical models and physical characteristics of three kinds of models representing welding heat sources are presented. Among them, Gaussian model and double ellipsoidal modelare used to analyze the thermal distributions with FE method. At the same time, this paper analyzed the influences of the heat source models, the latent heat,the welding parameters and the fluid flow of liquid metal on the temperature distributions. The comparisons between the simulated results with the experiments show double ellipsoidal model is good for three-dimensional numeral simulations. Furthermore, the adaptive mesh technique is applied in the three-dimensional numeral simulaton by producing a dense mesh of weld moving simultaneously with the heat source and a much coarser mesh in the other area of the structure which greatly reduces the number of nodes and elements in the simulation.