Abstract: The numerical model for thermodynamic and dynamic characteristics of reverse polarity plasma cutting was established. The results show that the plasma is heated and accelerated in the compressed channel of gun body, and the temperature and velocity of plasma reach the peak value, but the temperature and velocity of plasma are nearly constant for the diffusion region and the cutting cavity of the workpiece. The geometry of plasma gun body (nozzle diameter and compression channel length), process parameters (current, ion flow and nozzle height) have important effects on the temperature and velocity of plasma.