The invention discloses a fuel oil additive, which comprises the following components: 0.1 to 99.8 percent of dialkyl carbonate, 0 to 80 percent of ferrocene, 0 to 80 percent of benzotriazole, 0.1 to 80 percent of fatty alcohol and epoxyethane condensation compound, 0.05 to 50 percent of alkylphenol and epoxyethane condensation compound, and the like. The fuel oil additive can be widely used in gasoline of all grades, diesel oil, ethanol blended gasoline, biodiesel and heavy oil for various motor vehicles, marine diesel engines, diesel locomotives, industrial oil burning boilers and the like. The fuel oil additive has the advantages of improving the quality of fuel oil, increasing combustion efficiency, obviously saving oil, reducing harmful tail gases, strengthening the power of engines, protecting the engines, prolonging the service life of the engines, along with cleanness, no toxicity, small addition amount.