Abstract: A large amount of disorderly cooling air will be introduced into the boiler when the boiler dry-type slag removal system is running at low load, which will affect the stable combustion of the boiler and lead to the increase of flue gas temperature. Therefore, taking the dry slag discharge system of a 660 MW boiler as the research object, a cooling model of the dry slag discharge system was established, and on-site testing of the cooling air was completed. Combined with numerical simulation methods, the characteristics of the cooling air flow field in the dry slag discharge system were analyzed. A new cooling air control method is proposed by studying the cooling air flow field and temperature field through the closure of door switches. The results show that, after all the cooling air doors of the dry slag discharge system were opened, the proportion of head cooling air and horizontal section cooling air was the highest, both accounting for 79% of the total cooling air volume. The head cooling air is mainly affected by the opening of the cooling windshield, while the horizontal cooling air is mainly affected by the number of cooling air openings. The cooling air volume is not significantly affected by changes in furnace pressure. The increase in the number of cooling air openings in the horizontal and transition sections has little influence on the airflow of each hole. After closing the door 23 of the No.2 slag well, and doors 32 and 33 of No.3 slag well, the cooling air volume of the No.1 slag well is increased by 2.18 t/h and the average air temperature of the No.1 slag well is decreased by 9 ℃; when adding 2 sets of horizontal cooling air, the average air temperature of the No.1 slag well is decreased by about 100 ℃, which can obviously improve the problem of insufficient cooling of the ash layer below the No.1 slag well.