A diagnostic technique based on spectrographic analysis for nitrogen ion emission spectra was developed to measure the flame temperature distributions of solid propellants. The experimental equipment consists of a combustion chamber with a window, an optical scanning unit, a grating spectrograph, and data collection and treatment units. It has been applied to double base (DB), hydroxyl-terminated polybutadiene (HTPB), nitrate ester plasticized polyether (NEPE), and hexanitrohexaazaisowurtzitane (HNIW) propellants. The existence of the dark zone for a DB propellant could be revealed by this method. The highest measured flame temperature is comparable with the theoretical one and those obtained by thermocouple methods. The assumptions of the method and fluctuations in the temperature profiles are discussed. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.