Abstract: In the present work, computational fluid dynamics（CFD） numerical simulation method was used to study the combustion characteristics and pollutant emission characteristics of a 350 t/d municipal solid wastes（MSW） incinerator, with different blending proportions of semi-dried sludge（60% moisture content）. The selective non catalytic reduction（SNCR） denitration simulation was carried out and the position of spray gun was optimized. Results show that the gas temperature of the first flue gas channel is inversely proportional to the sludge blending amount, and the oxygen content is positively correlated. In 3% to 13% of the blending proportions, 7% is the appropriate sludge blending proportion and the combustion state in high temperature area of the first flue gas channel can satisfy the combustion requirements of dioxin control when the sludge blending amount is less than 10%. NO_x production is positively correlated with the proportion of sludge blending. In the case of 10% blending proportion, the NO_x content at the outlet of the incinerator is as high as 278.63 mg/m~3 when using the SNCR method alone, which fails to meet the emission standards. Focus on the vortex flow of flue gas, by adjusting the SNCR spray gun position of 10% blending condition, the denitration efficiency is improved and the NO_x content of the flue gas at the outlet under the same normalized stoichiometric ratio(2n_urea/n_NO) is reduced to 245.25 mg/m~3. The variation trend of temperature and NO_x under different sludge mixing amount is obtained by simulation calculation, the appropriate sludge blending proportion and SNCR spray gun layout optimization are put forward, which can provide reference for sludge blending incineration and SNCR denitration.