Abstract: In order to solve the problem of the increasingly tense situation of coal supply and demand in China, and to ensure the stability, economy and safety of boiler combustion to the greatest extent possible, the combustion characteristics of the boiler under different loads of mixed coal blending need to be studied, and the boiler combustion conditions need to be adjusted further optimally. A 1000 MW supercritical unit boiler is taken as the research object, and Meshing and Fluent modules in Ansys software are used to model the furnace, and numerical simulation is carried out to simulate the combustion process of Shenhua coal, Shenhua coal blended with Indonesian coal, and Shenhua coal blended with Russian coal in the furnace under the variable load condition, so as to analyse the influence of load change on the combustion characteristics of different coal types in the furnace. The results show that: at high load, the combustion in the furnace is sufficient and stable, but the flame in the furnace is more likely to wash the water-cooled wall, which is prone to local slagging; at low load, the flame in the furnace is poorly filled, and the stability of the cut-and-circle combustion decreases significantly, which is prone to the phenomenon of unburned fly ash. And with the reduction of load, the water-cooled wall ash pollution surface temperature is also gradually reduced, slagging tendency weakened, along the furnace height direction of the water-cooled wall heat absorption non-uniformity increases, when the load is further reduced to cause part of the burner group shutdown, the height of the flame centre will be reduced. The research results can provide basis and guidance for variable load and multi-coal blending in power plants.