Since the first 410t/h CFB boiler was built and put into business operation in 1996, CFB boiler has gotten a rapid development in China because of low emission and good availability for low rank coal. The CFB boiler technology has been selected to build a 300MW coal-fired boiler and to replace many pulverized coal-fired boilers with a capacity range from 220t/h to 410t/h in China. Most of these CFB boilers burn local low rank coals. To investigate the combustion characteristics of anthracite and optimize the operation of CFB boilers, a series of thermal tests were done on a 220t/h CFB boiler, in AIXI power plant, and on a 410t/h CFB boiler (the largest CFB boiler in China), in GAOBA power plant. The coal burned in these two CFB boilers came from the same coal mine. The properties of the boilers include: operating and designing parameters affected by the carbon content in the fly ash, the distribution of oxygen and temperature in the furnace, a limestone milling and transfer system, and operation under a lower load. All tests were aimed at how to optimize the operation of CFB boilers when anthracite is burned. Based on these test results, the technical requirements for a 300MW CFB boiler were investigated and are presented in this paper. The contents of the investigation included design considerations and ash utilization. An investigation on converting a pulverized coal-fired (PC) boiler to a CFB boiler is also presented in this paper. The content of the investigation includes basic design consideration of the conversion, and utilization of the milling system from an old PC boiler.