The invention relates to a flame retardant for a bituminous mixture based on decabromodiphenylethane. The flame retardant is characterized by comprising the following components: decabromodiphenylethane, antimony sesquioxide and metal salt, wherein the mass ratio of decabromodiphenylethane to antimony sesquioxide to metal salt is 4 : 1 : 1. When the suggested mixing amount of 8% is adopted, the synergistic flame retardant efficiency is 0.43, the limit oxygen index of SBS (Styrene Butadiene Styrene) modified asphalt is increased to 24.1% from 20.7%, and the smoke density level is reduced to 82.57 from 87.6.