This paper presents FE simulation of Arc welding process using nonlinear transient thermal analysis to study the effect of process parameters on temperature distributions in T-joint fillet welds. An APDL (ANSYS Parametric Design Language) program is developed to define moving surface heat source model with Gaussian distribution into simulations by using commercially available FE code ANSYS. The transient temperature distribution in fillet weld during welding process are predicted and subsequently validated with published experimental results. Influence of heat energy input, electrode angle, welding speed and plate thickness on temperature distribution was further explored. The present work provides a basis for prediction of welding residual stresses and distortions in fillet joints.