Abstract: The electron excitated temperature is one of the most important parameter of the plasma jet fluidics, and the testing results have great influence on other parameters. The plasma-arc is the representative of the plasma jet fluidics, so it is necessary to research the temperature field of the plasma-arc. In this paper, the authors provide a new technology which is used to diagnose the three-dimension temperature field of the plasma-arc by using orthographic and double-wavelength optical tomography. Firstly, the spectral intensity of the plasma-arc is collected using the CCD, which is placed on the two orthographic direction, then the emission coefficient distribution is reconstructed using the improved max-entropy algorithms; secondly, the spectrum relative intensity method is chosen to calculate the temperature field distribution based on the plasma physical theory; finally, the influence law under different parameter is analyzed. The research results show that this system can realize the three-dimension temperature field reconstruction, the testing precision is high and the result is real time. It provides good theoretical and experimental basis for the further understanding of the inner machanism of the plasma-arc.