Abstract: At present, the main source of carbon emissions from energy consumption in China is coal power, and biomass power generation can be regarded as a zero-carbon power generation method, and coal-fired coupled biomass power generation technology can help reduce carbon emissions from thermal power units. In order to realize the co-grinding coupling direct co-firing of biomass particles in coal-fired boilers under low load, the co-firing experiments of biomass particles (corn straw) with different proportions (mass ratios : 3%, 5%, 7%, 10%) were carried out in a lignite boiler of a 600 MW unit. Through the operation test of boiler and pulverizing system, the influence of co-firing biomass particles on the pulverizing, combustion and emission characteristics of boiler was studied and analyzed, and the maximum co-firing ratio of single coal mill and boiler was determined. The results show that under the medium and low load (320 MW), when a single mill is mixed with 10% biomass particles, the output of the pulverizing system decreases, the grinding phenomenon occurs, and the operating current exceeds the limit. With the increase of the blending ratio, the uniformity of pulverized coal fluctuated, and the uniformity index was lower as a whole, but it was not obviously affected by the blending of biomass particles, the pressure difference between the inlet and outlet of the coal mill increased, and the volume fraction of CO remained below 80×10⁻⁶. The maximum blending amount of 7% had little effect on the milling performance and safety. Compared with lignite combustion alone, the ignition temperature and burnout temperature after burning biomass pellets were reduced, and the combustion performance of lignite was improved. Under lower load (240 MW), the whole furnace blended with 7% biomass pellets will not reduce the combustion performance of the boiler. NO_x and SO₂ emissions are little affected by blending, and the treatment capacity of the environmental protection facilities of power plant units can fully ensure that the conventional pollutants meet the ultra-low emission standards after blending with biomass pellets. According to theoretical calculations, the blending of 7% biomass under a load of 320 MW can reduce CO₂ emissions by 17.1 t/h, and the carbon emission reduction effect is significant.