In order to improve the accuracy and usefulness of CCD-based measurement of Flame Radiant Energy (FRE) and apply it to the boiler combustion control system, a new method of obtaining FRE is proposed. According to the principle of CCD imaging and radiation heat transfer theory, the mechanism model of the FRE is derived. Then based on this model and a large number of experimental data, we can apply nonlinear least square method to identify those unknown parameters, so the function of FRE, RGB and the flame area can be determined. The experimental results show that the maximum relative error of the fitting model is 1.38%, and the correlation coefficient of the true values and the fitting values is 0.9978. The accuracy of the model meets the industrial application requirements with strong engineering practical importance and extensive application prospect.