The furnace inner temperature is an important parameter, it is important characteristic index the boiler inner burns process and the gas discharging. Analyzed the CCD camera measuring mechanism, built the mathematical model of calculating burning temperature field from flame image, deduced and built tricolor temperature measuring model. At the same time, it introduces the way of extraction of flame intensity grade. Experiments and simulations show that the way getting combustion temperature field from flame image has more high measurement precision and bright prospect industrial application. It is a fundamental work for the operation of the burner hearth optimized and automatic control.