Provided is a method for measuring temperature of long-gap air arc plasma, relating to heat plasma temperature measurement field. The method is based upon spectrum diagnosis principle of air arc plasma radiation, shooting long-gap air arc image through an attachment double-narrow-band-pass filter and a calibrated color CCD high speed image acquisition system, and storing in BMP format which data is not compressed; correcting pixel value of arc color bitmap file responded with two feature center wavelengths to original data of arc radiation intensity; obtaining arc radial light intensity distribution through Abel transformation, then calculating arc plasma projection temperature distribution or arc plasma temperature radial distribution by a colorimetry of spectrum relative intensity, and rebuilding tridimensional temperature field. The method of the present invention can measure open arc plasma temperature in air of several meters accurately and provides an important plasma parameter for researching microcosmic mechanism of long-gap air arc.