Abstract: The behavior of arc is affected deeply by energy. The study on energy dissipation of GMAW arc in high pressure environment is of great importance to guide welding process and improve arc stability. The energy loss of the arc is difficult to be measured directly. Therefore, the heat flow of the cylinder at a certain distance from the center of the arc is used as a reference to compare the energy loss of GMAW arc under different pressures. Based on the hydrodynamics and heat transfer theory, a numerical analysis model of the high pressure GMAW was established to calculate the external energy transmission of the local area of the arc. The experimental platform of high pressure GMAW energy dissipation measurement was established, and the energy transmission of the whole cylinder was obtained by collecting the energy transmission amount of 1/16 cylinder for conversion, and the measured results were corrected by using the natural convection heat transfer model of the circular tube. The influence of ambient pressure on arc energy dissipation is analyzed by comparing the simulation and experiment results. The results show that the external energy dissipation of GMAW arc increases, The high temperature region of the arc gathers towards the center of the arc, and the arc appears to shrink at the same time. with the increase of ambient pressure, the energy dissipation of the arc near the cathode region enhances more, and the arc shrinkage in the cathode region is more obvious, which is one of the inducement of the instability of the high voltage GMAW arc.