Abstract: Aimed at Ar-N₂ plasma welding arc, a mathematic model was established according to the theory of magnetic fluid dynamics. PA welding arc was numerically analyzed by the 3D, static and axisymmetric model with ANSYS software.The temperature, electromagnetic force and velocity profiles of the Ar-N₂ protecting arc have been simulated.The characteristic of the Ar-N₂ protecting plasma welding arc was analyzed and compared with the Ar protecting plasma arc.The results show that with the mixed plasma gas the maximum temperature of the arc is higher than that of the Ar plasma arc.And the maximum temperature area leans to the anode.