Abstract: In recent years the numerical calculations of welding tempeiature field have been got prcgress.Most of them were calculated by linear finite element equaticns or difference equations.In this paper,we analysis the non-linear heat conducting problems by FEM,establish the calculated model of instantaneous welding temperature field and compile the relevant computer programs.In these programs,the heat transfer conditions of surface and the variation of thermal physical property that depend on temperature have been considered.The two-dimensional temperature field of thin or thick plate caused by fixed or moving source during quasi-stable or non-quasi-stable conditions can also be analyzed by FEM.In this paper,the temperature fields caused by fixed or moving source of thin plates butt welding have been analyzed as exemples.The results show the calculated accuracy can be improved when the temperature dependent thermal physical property and heat transfer condition of surface were considered.The analysis also show that the temperature distribution of weld metal and the nearby zone is tending towards quasi-stable if the provided calculated model size is suitable.