Abstract: To grasp the influence of complex coal on the slagging of the water-wall and carry out anti-slagging of the coal blending optimization, the species transport model was used to carry out a three-dimensional numerical simulation of the combustion process of a 330MW tangential firing boiler, studying the effects of the three types of coal on the slagging of the water-wall under different blending methods——I(high ash content for A_ar is higher than 35%, low calorific value for Q_{ar, net} is lower than 15.5MJ/kg), Ⅱ (medium ash content for A_ar is between 25% and 35%, medium calorific value for Q_{ar, net} is between 15.5MJ/kg and 19.7MJ/kg), and III(low ash content for A_ar is lower than 25%, high calorific value for Q_{ar, net} is higher than 19.7MJ/kg), and performed slagging evaluation and coal blending optimization. The study found that the area and degree of slagging on the water-wall caused by temperature under different coal blending methods were roughly the same, but the difference of slagging on the water-wall due to CO concentration was greater. Compared with the coals blending outside the boiler furnace, the CO concentration changed more when the coals were blended in the boiler furnace. To reduce the slagging, when coals are blended in the furnace, it is recommended that the bottom two layers of the burner adopt coal of type II, the 3rd and 4th layers of the burner adopt coal of type I, and the uppermost layer of the burner adopts coal of type III. When coals are blended outside the furnace, it is recommended that the bottom two layers of the burner adopt coal of types I and II, the 3rd and 4th layers adopt coal of types II and Ⅲ, and the uppermost layer adopts coal of types I and III, the best blending ratio of each coal type in each layer of burner is 1:1.