The invention discloses a method for simultaneously desulfurizing, denitrating and purifying 
flue gas and belongs to the field of 
flue gas purification. The method comprises the following steps: spraying the 
flue gas at the temperature of 50-90 DEG C by using 
ammonia absorption liquid to obtain a solution, and aerating and oxidizing the solution to obtain an 
ammonium sulfate solution; exchanging heat between the obtained 
flue gas and the original 
flue gas, heating to 120-350 DEG C, and supplementing 
ammonium hydroxide; converting NO and NO2 in the 
flue gas into N2 by addition or non-addition of an 
activated carbon material of a catalyst; performing reaction on the remaining SO2, 
ammonia and 
water vapor to generate 
ammonium sulfate; adsorbing mercury, dioxin, 
furan, a 
volatile organic compound, 
ammonia sol and other trace toxic substances by 
activated carbon; and regenerating the 
activated carbon after absorption and adsorption by using washing and heating methods. The method has the advantages that the process is simple and convenient, and the desulfurizing and denitrating efficiency is high; various toxic substances and fine particles in the flue gas can be adsorbed, a good prevention effect on PM2.5 
pollution of industrial flue gas is achieved, 
ammonium sulfate and 
ammonium nitrate fertilizer byproducts are obtained, and resources can be recycled. The method can be applied to purification of 
sulfur-containing and 
nitrate-containing flue gas in the fields of boilers, 
metallurgy, 
chemical industry, thermoelectricity and garbage 
incineration power generation.