Waist air distribution is mainly used for the combustion of inferior coal. This air distribution method can reduce the oxygen content in the main combustion zone, correspondingly increase the pulverized coal concentration in the main combustion zone, and ensure the temperature level of the main combustion zone, so as to ensure the normal ignition and stable combustion of pulverized coal airflow. In this sense, it is similar to improving the heat load of the furnace section in this combustion zone and becoming a stable combustion zone of the furnace flame.