Abstract: In order to study the influence of the secondary air injection angle on the temperature, speed, flue gas residence time and exhaust heat loss in the furnace of the incineration boiler and the correlation between the secondary air injection angle and the NO_x concentration at the incinerator outlet, the UDF compiler boundary condition and Fluent coupling method were adopted. The secondary air injection angle of front and rear walls of a 600 t/d municipal solid waste incineration boiler was numerically simulated. The simulated variation range of the front wall secondary air injection angle was 68°-80°, the variation range of the rear wall secondary air injection angle was 61°-73°, the secondary wind speed was 42 m/s, and the secondary air temperature was 301.15 K. The results showed that when the secondary air injection angle of the rear wall was constant, the NO_x concentration increased first and then decreased with the increase of the secondary air injection angle of the front wall. The minimum concentration of NO_x was 142.23 mg/m³, the heat loss of exhaust smoke from the incineration furnace was reduced, and the minimum heat loss of exhaust smoke was 7.12%. When the secondary air injection angle of the front wall remained unchanged, the NO_x concentration increased first and then decreased with the increase of the secondary air injection angle of the rear wall. The minimum concentration of NO_x was 149.15 mg/m³, the heat loss of exhaust smoke from the incineration furnace increased first and then decreased, and the minimum heat loss of exhaust smoke was 7.46%. When the secondary air injection angle of front and rear walls was 80° and 67°, respectively, the average temperature between the two layers of SNCR spray guns was 1 229.59 K, and the residence time was 1.63 s, which was closer to the optimal reaction temperature and residence time of SNCR denitrification compared with other conditions. The average temperature at the exit of the first flue was 1 211.36 K, and the residence time was greater than 2 s, which helped to inhibit the formation of dioxins.