The scale of new energy power generation such as wind power and photovoltaics continues to grow rapidly,and the peak-to-valley difference of grid load continues to increase,as a result,the peak shaving operation of coal-fired thermal power units has become more frequent. In order to study the key influencing factors in the actual peak-shaving operation of coal-fired units,the peak-shaving test of 8 coal-fired units with different types was carried out. In the test,the stable combustion ability of the boiler under the deep peak regulation operation state was analyzed by measuring the negative pressure of the boiler furnace,the fire detection signal and the state of the combustion-supporting measures. The pollutant emission concentration of the coal-fired unit under the low-load operation state,and the variation law of the temperature of the SCR flue gas denitrification device under different loads was also analyzed. In addition,the relationship between the heat supply of the extraction steam heating unit and the peak regulation capacity was studied,and the effect of unit heat supply on peak shaving performance was analyzed. The results show that when the coal quality is close to the design coal quality,most units can achieve stable operation below 40% of the rated capacity under pure condensing conditions,which is close to the unit′s design minimum stable combustion load;NOx emission has become an important limiting factor during the deep peak-shaving operation of coal-fired power units. The operating temperature of the SCR denitrification device may drop below 300 ℃ under low load,which will seriously affect the normal operation of the SCR device and restrict the deep peak shaving operation of the unit.The small heat supply of the unit will help to improve the low-load operation of the boiler.However,when the heat supply is large,it will seriously affect the deep peak shaving of the unit,which may reduce the peak shaving capacity of the unit by more than 20%.