Abstract: Temperature field distribution of the arc in microplasma arc welding was simulated by ANSYS software, and the calculation results was validated by the spectral measurement and the image processing of high-speed photography. The results showed that the axial maximum temperature of the arc in microplasma arc welding occurs in the area near the tungsten cathode, and the arc temperature decreases with the increasing of the distance from the tungsten tip. The maximum radial temperature of the arc in micro-plasma arc welding occurs at the center of the arc transverse, and the temperature decreases with the increasing of radial distance from the center of the arc transverse. With the increasing of welding current, the axial maximum temperature in the area near the tungsten tip and the radial maximum temperature at center of the arc transverse increase. With the decreasing of tungsten tip diameter, the axial maximum temperature in the area near the tungsten tip and the radial maximum temperature at center of the arc transverse increase. After normalizing, the numerical calculated radial and axial temperature distributions have high agreement with distribution results by using spectrum detection and image processing of high-speed photography, respectively.