The invention discloses an efficient herbicide and a preparation method thereof. The efficient herbicide comprises the following raw materials in parts by weight: 10-20 parts of bensulfuron methyl, 20-30 parts of sodium hexametaphosphate, 20-30 parts of 1,4-diphenyl acetophenone, 10-15 parts of ammonium nitrate, 40-50 parts of urea, 10-18 parts of citric acid, 20-40 parts of sodium nitrate, 23-30 parts of dioxymethane, 10-25 parts of methyl ethyl ketone, 27-30 parts of butyl acetate, 20-50 parts of methyl isopropyl ketone, 5-10 parts of a surfactant and 40-80 parts of water. The preparation method comprises the following steps: heating thebensulfuron methyl, the sodium hexametaphosphate, the 1,4-diphenyl acetophenone, the ammonium nitrate, the urea, the citric acid, the sodium nitrate, the surfactant and the water to react; adding residual components; and continually heating and reacting, and cooling. The efficient herbicide disclosed by the invention has high activity and good activity and has a serious growth inhibition effect on weeds.