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Most of the simulation models about arc plasma are based on the hypothesis of local thermal equilibrium (LTE). The nonequilibrium model is very complicated due to the calculation of electron temperature. In this paper, an improved LTE model is developed and applied to the 3-D simulation of the flow patterns inside a nontransferred dc arc plasma torch. Numerical calculations on the distributions of gas temperature and velocity in the plasma torch were carried out using argon as the plasma gas. The electric current density and potential are also discussed. The results indicate that the temperature and velocity distributions of the arc are almost axisymmetrical. The results of voltage drop agree well with the experimental observations. It seems that anode erosion is located on the internal surface of the anode, where the largest number of electrons is injected.