The invention relates to a multifunctional raw gas purifying agent, a preparation method and an application method thereof. According to the present invention, active alumina is adopted as a carrier, and the carrier loads ammonium molybdate, one or two materials selected from copper acetate, zinc acetate, lead acetate, nickel oxalate and ammonium metavanadate, and one material selected from magnesium chloride, potassium carbonate and sodium carbonate to prepare the multifunctional raw gas purifying agent, wherein the mass of the loaded ammonium molybdate is 1-10% of the mass of the carrier, the total mass of the other two or three loaded metal compounds is 10-25% of the mass of the carrier. The preparation method for the multifunctional raw gas purifying agent comprises: impregnating the carrier for 2-6 hours by the metal compound solution; drying for 2-4 hours at a temperature of 120 DEG C; carrying out baking for 4-6 hours at the temperature of 280-350 DEG C to prepare the multifunctional raw gas purifying agent. The multifunctional raw gas purifying agent of the present invention is adopted in the raw gases of water gas, semi-water gas, coke oven gas or IGCC power generation fuel gas to purify COS, CS2, HCN, SO2, SO3 O2 and other impurities, wherein the conversion rates of the COS, the CS2, the HCN, the SO2 and the SO3 are more than or equal to 90%, and the O2 removal rate is more than or equal to 95%.