This paper presented a model for simultaneously measuring the two-dimensional temperature and particle concentration distribution from the images of the flame. In order to determine the relationship between a point in the three-dimensional space and its image in the camera, the optical image-formation process was analyzed. The inverse problem of the radiation transfer in the participating medium was studied. The mathematics method to simultaneously solve the temperature and the particle concentration was discussed. To validate the model presented in this paper, a test furnace with the fuels mixed by pulverized-coal and oil was set up. The temperature and particle concentration of a cross section were measured under different coal feed rates. The comparison between the measured temperature by the pyrometer and the calculated temperature according to the flame image proved that the two-dimensional distribution of temperature can be obtained accurately. The particle concentration distribution was reasonable under different cases. (c) 2009 Elsevier Ltd. All rights reserved.