We have developed a reconstruction algorithm for non-contact measurement of temperature and absorption of combustion gas distributed in a flame. To get accurate temperature distribution of the combustion gas, the absorption of the gas must be known. We achieve this by obtaining the projections of thermal radiation from the flame and an external radiation source which is turned on and off while obtaining projections. We can reconstruct the distribution from the projections by using an emission computed tomography (CT) algorithm. We have developed a prototype measurement system and made some experiments to measure temperature and absorption distribution of methane-air flame of a Bunsen burner