The flame image monitoring technology based on CCD is a research focus of the boiler combustion control, and the key of this method is to obtain a clear and reliable flame color image. In response to this demand, wavelet analysis and dual-threshold method are used to enhance flame color image. Firstly, the color image is decomposed into three two-dimensional RGB signals. Secondly, the RGB signals are processed through wavelet transform respectively, and those wavelet coefficients are amplified and reduced using dual-threshold method for the purpose of enhancement and denoising. Then, the new RGB signals are reconstructed by those wavelet coefficients. At last, the new RGB signals are regrouped to get enhanced flame color image. Experimental results show that, after processed by this method, the image has a strong sense of hierarchy, detail of image is outstanding and the distinction of the combustion zone of the flame is obvious. Moreover, measurement precision of two-dimensional temperature field is improved by 0.62% and the absolute error is reduced by 5.3℃. This is helpful to improve the performance of the boiler combustion control system.