Abstract: Calculations were made for the transient solution of welding thermal process with a point heat source moving on the workpiece with three different energy distribution models based on point heat sources for gas metal arc welding,(GMAW) process.These three distribution models of energy input for GMAW process were evaluated by the comparison between the predicted weld junction and the measured results.Moreover,weld junction of the weldments from low carbon steel Q195 and low alloy steel JG590 via GMAW technique were predicted using the developed string heat source model.Experiments for both Q195 steel and JG590 steel were conducted.The predicted weld cross sections had a good agreement with the experimental measurements.Current equations for t_8/5 calculation were evaluated.Based on the calculated results from GMAW thermal process,microstructure and hardness of JG590 steel fusion zone were successfully predicted with the continuous cooling transformation diagram.