In high temperature furnace, the diluted combustion with inert gas occured, in response to the influence of radiation of the wall used as a background, optical flame diagnosis will become more difficult. Then, as a result of examining the intensity ratio of two spectrums of spontaneous chemiluminescence of the same radical OH in UV region with little this influence. As for a energy distribution function of molecule, it turns out that it is close to heat balance conditions, and we can show possibility that the temperature of only gas could be measured remotely even if there is respectively strong radiation.