Abstract: Based on the theory of Magneto-Hydrodynamic (MHD), the arc numerical models of micro TIG spot welding with tungsten electrode radius of 0.8 mm and tip cone angle of 15°, 30°, 45° and 60° were developed. The source terms of momentum equation and energy equation and the conductivity of argon gas were loaded by the User Defined Function (UDF) of Fluent software to investigate the influence of tungsten tip cone angle on the temperature, flow, pressure and potential fields of the micro TIG arc. The results shows that the micro TIG arc is bell-shaped, and as the taper angle decreases from 60° to 30°, the radius of the tungsten conductive section decreases, leading to an increase in current density and an increase in arc temperature. As the taper angle continues to decrease, the arc creeps upward, the tungsten conductive area increases, the average current density decreases, and the arc temperature decreases. The change of tungsten taper angle significantly affects the plasma flow force and electromagnetic contraction force on the arc plasma momentum, which in turn affects the arc plasma motion velocity and anode surface pressure distribution. The numerical simulation results are in good agreement with the experimental results of micro TIG spot welding, and the simulation results are of great significance in regulating the tungsten cone angle and improving the arc shape and welding quality.