CFD simulation has been applied many engineering areas such as automobile, electronics and so on, including energy industry. In this study, CFD analysis and its application to the energy industries, especially for the design of reactor design, has been carried out. CFD analyses for the furnace of fossil power plant and combustion chamber of incineration plant have been done to check appropriacy of geometrical design and/or given operating condition. These analyses were research oriented because of dificulties to take risk of modifying large size plant. However, CFD analysis results of SCR reacor and/or its auxiliary equipments were directly used for the basic design because analysis itself is very easy due to its simple fluid flow behavior without chemical reaction. CFD analysis of coal gasification was conducted to develop entrained bed coal gasifier based on new concept of compactness. Aspect ratio of 3 ton/day-scale gasifier was checked and swirl angle of multiple-burners was designed from the CFD results. High cold gas efficiency and carbon conversion were achieved within short residence time.