Abstract: A three-dimensional mathematical arc model in keyhole PAW (plasma arc welding) process was established based on the mass, momentum and energy conservation equations.Magneticvector method was employed to solve the magnetic problem.A part of nozzle and tungsten electrode, as well as keyhole, were included into the model.The model was solved with ANSYS software.The simulated temperature was taken to indicate the arc reflection occurring in PAW processing.The plasma arc can be divided into main body, arc reflection and arcwake flame, which can be obtained from the simulated result.The effects of the keyhole dimension and offset between the arc axis and keyhole axis on the arc reflection were studied.The simulated results show that the arc reflection gets weaker and arc wake flame gets stronger with the increase of keyhole dimension, and a higher welding velocity to induce the offset between the arc axis and keyhole axis is necessary to the appearance of arc reflection, and the effects of welding current on the arc reflection are exentedmainly through changing the keyhole dimension.