The action of the composite heat source model in DE-GMAW has been carried out according to the characteristics of the DE-GMAW process,and the distribution of surface and body heat source was analyzed.The weld temperature field distribution has been derived from the appropriate boundary conditions and the thermal physical property parameters by COMSOL software.The effects of the positions of the surface and body heat source on the crosssectional shape were investigated by studying the experimental welding thermal cycle curve.The simulated results are fully compliant with the experimental data under the same conditions.This illustrates that the composite heat source model is correct.It reflects the thermal mechanism of DE-GMAW process,and reveals the internal influence of weld shaping. The action of the composite heat source model in DE-GMAW has been carried out according to the characteristics of the DE-GMAW process, and the distribution of surface and body heat source has been analyzed. The weld temperature field distribution has been derived from the appropriate boundary conditions and the thermal physical property parameters by COMSOL software.The effects of the positions of the surface and body heat source on the crosssectional shape were investigated by the experimental welding thermal cycle curve. The simulated results are fully compliant with the experimental data under the same conditions. This illustrates that the composite heat source model is correct. It reflects the thermal mechanism of DE-GMAW process, and reveals the internal influence of weld shaping.