Nitrogen protecting tungsten inert gas(TIG) welding arc was studied.A mathematic model was developed according to the theory of magnetic fluid dynamics.The electrode tip geometry is consi-dered in the model,and the TIG welding arc was numerically analyzed based on this model.The calculated result of arc plasma temperature agrees with the experiment,and is compared with Ar protecting arc at the same condition.The arc pressure,current density distribution and velocity distribution were analyzed based on the m...