In order to carry out the flame visualization and combustion intelligent diagnosis on pulverized coal furnace, and then give the instruction information for power plant staff, we have established a flame image processing and combustion diagnosis system based on Web. In this paper, firstly we propose a kind of browser/server three-layer structure based on Web and Java, then analyse the advantages of this kind of structure in detail. We apply this structure to the flame image processing and combustion diagnosis system . We use optical lens?CCD camera and image card converting the flame video signal to digital signal. By utilizing the flame image processing method and the radiation information of the furnace , we can monitor and analysis the state of combustion and the product of NOX on line. We have developed measurement of project temperature based on colorimetric method and reconstructed section temperature field in terms of ART(Algebraic Reconstruction Techniques). This system has appplied in two of the power plants, effectively improving the level of automatic supervising and safety in the power plants.