An innovative numerical model was established to study the heat transfer mechanism with cold metal transfer plus pulse (CMT+P) composite heat source based on the in situ observation experiments as well as theories of electromagnetic dynamics, fluid dynamics, and thermodynamics. The distribution of temperature, potential, current density, velocity, and pressure within the arc plasma was quantitatively analyzed. The results show that the physical fields of the arc plasma with CMT+P composite heat source, such as temperature, electricity, velocity and pressure, were related not only to the input current, but also to the discharge distance between the electrodes. The closer the physical fields of the arc plasma were to the anode, the faster response rate to the current variations and the weaker time delay effect. In addition, the closer the distance between two electrodes, the more concentrated the temperature. There was a negative correlation between the distribution of potential and current density corresponding to the surface of the molten region at different moments. With the completion of the short-circuit phase, the arc plasma was reignited and converged towards the wire end under electromagnetic pinch force. The high-speed axial vortices were generated again at the wire end, which promoted the shrinkage of the liquid metal section and accelerated the splashing of free droplets. Moreover, the distribution of temperature, potential, current density, pressure, and velocity on the substrate surface had a time delay effect with the input current during the pulse phase.