Abstract: Temperature distributions calculated by finite element method will affect the microstructure, mechanical properties and residual stresses of materials. The exact solution for welding temperature field is prerequisite for analyzing metallurgical process, calculating stress and deformation and controlling welding quality. A three-dimensional finite element model has been developed with the SYSWELD FE code to simulate the temperature distributions in low carbon low alloy steel of T-joint during welding process. Various phenomena associated with welding, such as temperature dependent material properties, heat loss by convection and radiation and latent heat, are taken into consideration. The influence of the heat transfer coefficient on the temperature distributions is analyzed. The temperature distribution at various times and the thermal cycles at different locations are researched. The results are discussed properly and verified. The calculated results are in agreement with the experimental-measured values.