Abstract In this paper, a heat transfer model of the filler wire in twin-body plasma arc welding (TPAW) was established. The total power transferred to the filler wire included anode effect power, resistance power and plasma arc power. The influences of the wire current, wire extension and plasma gas flow rate on the power transferred to the filler wire were studied using the location of the molten region of the filler wire as the characteristic parameter. The studies showed that the anode effect power caused by the increase in wire current can increase the total power transferred to the filler wire by 50 % or more while the current flowing through the tungsten electrode of the plasma torch remains constant. This is confirmed by analyzing the weld shape under different wire currents. The resistive heating of the wire excision is not a major component of the total power transferred to the filler wire, and the wire extension can be set to a reasonably wide range of values. There was a threshold value for the influence of the plasma gas flow rate on plasma arc power. When the plasma gas flow rate was greater than the threshold value, plasma arc power remained nearly constant as the plasma gas flow rate increased. Therefore, the total power transferred to filler wire in TPAW was composed of anode effect power and plasma arc power.