For the high combustion temperature measurement in harsh environment, the radiation spectroscopy method was proposed to realize the online measurement of combustion temperature of solid rocket propellant. The radiation spectrums in the range of 200~1 100 nm of solid rocket propellant flame in high pressure experimental combustor were obtained by fiber-optic spectrometer. Their representative characteristics were summarized, and the corresponding combustion temperature was determined by the Planck radiation law and the spectral fitting method. The paper provides important reference for combustion diagnostics and mechanism of solid rocket propellant.