In order to further improve the capacity of thermal power units to absorb new energy,the demand for peak load regulation of thermal power units becomes higher and higher. Taking a 330 MW subcritical circulating fluidized bed unit of a power plant as an example,the corresponding operation strategies and technical measures were put forward to solve the problems of fluidization safety,high pollutantemission concentration and working medium deviation that restricted the realization of deep peak shaving. By changing the spacing of screen plate spacer bars to 8 mm,the coal particle size entering the furnace can be reduced.A throttle ring of "return" shape was installed on the wind cap,which improved the fluidization state of the unit under deep peak shaving. By adjusting the area of the air distributor and the ratio of primary air to secondary air,the minimum fluidizing air volume during deep peak shaving can be effectively reduced. After adjustment,when the fluidizing air volume is 380 km3/h and the air temperature is 245 ℃,the resistance of the air distributor is increased by 2 231 Pa. Under 50% load,the average temperature difference before and after the fluidized bed decreases from 126.8 ℃ to 27.2 ℃. The flue gas recirculation system was introduced,which was retrofitted with multi fluid multi particle furnace desulfurization technology and denitration lance. 300-500 μm limestone was sent into the furnace by secondary air,and 1-2 mm limestone was sent into the furnace by coal feeding. The multiple groups of denitration nozzles were installed in the direction tangential to the middle and lower part of the furnace and the slope of the secondary air outlet,and the switches of the denitration nozzle were adjusted according to different peak loads. When 20% of the units are operating at the depth of peak shaving,SO2 emission can be stably controlled within 5 mg/m3,NOx emission can be reduced to below 30 mg/m3,and the original water cooling shield is transformed into a small area parallel type to reduce the flow deviation and temperature deviation of the working medium. The boiler unit shall be subject to pressure fire protection test to maximize peak load regulation. The research results can provide reference for the deep peak shaving operation of coal-fired boilers at the same level.