Abstract: The numerical model of hollow tungsten TIG welding with inner diameter of 2 mm is developed. The source terms of momentum equation and energy equation and the conductivity of argon gas are loaded by the user defined function (UDF) of Fluent software. The temperature field, flow field and arc pressure are calculated when the welding current is 60 A in steady state. The results are compared with those of solid tungsten TIG arc under the same conditions. The results show that the shape of hollow tungsten TIG arc is bell jar shape, and the temperature field is concave at the top middle position due to the air flow and current density. The velocity of plasma below the tungsten pole is faster than other regions. The arc pressure is uniformly distributed, and the anode surface pressure is uniformly distributed in cylindrical shape. Compare with TIG welding under the same current condition, the maximum temperature, maximum plasma flow velocity and peak arc pressure of the hollow tungsten arc are reduced by 17.3%, 40% and 57%, respectively, and the peak temperature of the 2 mm cross section below the tungsten electrode is reduced by 27%. The weld width of surfacing welding increases by 30% but the weld depth decreases by 27.9%.