According to the actual operation data from a mixed waste fired power plant in Shanxi province, the model of pollutant emission process of boiler burning waste, coal and straw was established. Validation showed the model can better simulate the process of mixed fuel boiler pollutants emissions. The multi-objective optimization function of flue-gas pollutants emission was designed and the Pareto optimal solution set was found. According to the engineering condition of dioxins could be broken down when the mixed fired temperature was in the range of 850~900℃，the efficient solution subset of boiler mixed burning operating condition that emission values could satisfy the engineering requirements was further selected from Pareto optimal solution set. The subset showed that when the temperature was higher than 850℃,with appropriate increase of the blending amount of coal and temperature, the formation of dioxins of boiler side exit has been significantly reduced, the minimum was 0.0128ngTEQ/m3, far better than the national standard value of 1.0ngTEQ/m3 of eventually allowed emissions gas and test value 0.026ngTEQ/m3 of the on-site gas after purification. Moreover, the other pollutant emission value is also much lower than the actual test value of side exit of on-site boiler.