Abstract: A 600 MW supercritical before and after hedge combustion boiler is taken as the research object. The boiler coal is replaced from lean coal to low ash melting point bituminous coal. The study found that the combustion system transformation should reduce the heat load of the burner area, so as to prevent the high temperature of the burner area from leading to serious coking of the furnace. At the same time, the heat load of the burner area should not be reduced too much to prevent the flame center of the furnace from moving up, resulting in the screen superheater dreling, reheater overtemperature, large temperature water reduction, insufficient stable combustion capacity and other problems. The upper burner is raised 2 500 mm, and the middle burner is raised 500 mm. After the transformation, the spacing between the upper burner layer is 6 742 mm, and the spacing between the middle and lower burner layer is 5 242 mm. Through the burner unequal spacing arrangement, the wall heat load of the burner under THA conditions can be greatly reduced to 1. 39 MW/m~2; 50% load and above, the main steam temperature reaches 571 ℃, the reheat steam temperature reaches 569 ℃, the boiler efficiency is greater than 94%, the furnace outlet flue gas temperature is 1 000 ℃, and the high inlet flue gas temperature is 984 ℃, which is lower than the melting point of coal ash, which can prevent the heating surface coking and coking near the burner. The maximum CO concentration at the outlet of the economizer is 180 μL/L, the maximum NOx concentration is 235 mg/m~3（N）, and all the parameters meet the requirements of the transformation target.