Abstract: Base on Saha equation, the arc plasma particles' density is obtained, and then according to the theory of Kramers-Unsöld, the radiation intensity of arc is obtained.In order to get the model of arc radiation, the location of temperature measurement has been built.The ratio of signal to noise is used to analyze the effect of arc on radiation thermometry which the three factors of the angle of temperature detector, wavelength and the arc effective temperature are considered.Theoretically, the method of temperature measurement is feasible when the arc current is decreased to a smaller value in welding process.Experiment has been done;temperature data of three times which are peak value of arc current, least value of arc current and time of cutting arc current instantaneous have been collected. The experiment results show that the method of temperature measurement is feasible.