The invention relates to a system and a method for efficiently and economically processing the coal ash and bottom slag of coal-fired units of power plants. At present, a pressing system and a processing method which can effectively guarantee the quality of uniformity of coal ash do not exist. The system is characterized in that: the system comprises a coarse ash silo, a coarse ash silo dust collector, coarse ash silo level indicators, an ultrafine coal ash mill, a pneumatic coarse ash silo gate valve, a lifter, an ash-milling dust collector, a finished fine ash silo, a mill sampler, a coarse ash and fine ash separator, a mill ash trap, a mill divider, a dust collector sampler, a raw ash silo and a secondary ash silo, the coarse ash silo is connected with a heated boiler tail surface coal saver and an air preheater, the coarse ash silo dust collector and the coarse ash silo level indicators are mounted on the coarse ash silo, the ultrafine coal ash mill is connected with a power plant coal-fired unit pulverized coal furnace and the coarse ash silo, the pneumatic coarse ash silo gate valve and the lifter are mounted between the coarse ash silo and the ultrafine coal ash mill, the ash-milling dust collector, the finished fine ash silo, the mill sampler and the coarse ash and fine ash separator are connected with the ultrafine coal ash mill, the mill ash trap is connected with the mill sampler, the mill divider is connected with the mill ash trap, and the dust collector sampler, the raw ash silo and the secondary ash silo are connected with a power station coal-fired unit electrostatic precipitator. The invention can effectively guarantee the quality and uniformity of coal ash.