NOVELTY - A phytocide diuron is prepared by adding aromatic compounds solvent into reaction unit, introducing phosgene, adding dimethyl formamide, dropping solution containing 3,4-dichlorobenzene isocyanate and aromatic compounds solvent, adding solution containing triethylene diamine and aromatic compounds solvent, and obtaining solution containing 3,4-dichlorobenzene isocyanate and aromatic compounds solvent; and adding the obtained solution into reaction unit, and dropping dimethylamine aqueous solution, 3,4-dichlorobenzene isocyanate and dimethylamine.    USE - Method for preparing phytocide diuron (claimed).    ADVANTAGE - The method can make a total recovery of more than 91% of napropamide using dimethyl formamide as catalyst and triethylene diamine as promoter. It has low cost and high quality, is more environment-friendly, and is safer.    DETAILED DESCRIPTION - Preparing phytocide diuron comprises:    (A) adding aromatic compounds solvent into reaction unit containing exhaust gas treatment system, stirrer, condenser pipe, air-taking tube and thermometer, cooling to - 15 to - 30 degrees C, introducing phosgene for 0.5-2 hours, stopping cooling, adding dimethyl formamide and introducing phosgene, dropping solution containing 3,4-dichlorobenzene isocyanate and aromatic compounds solvent, heating to 20 degrees C, finishing dropping within 0.5-2 hours at 20-50 degrees C, keeping warm below 20-50 degrees C and stirring for 0.4-1 hour, stopping introduction of phosgene, slowly heating to 90-100 degrees C, adding solution containing triethylene diamine and aromatic compounds solvent, keeping warm for 2-4 degrees C, introducing nitrogen, purging excess phosgene and hydrochloric acid gas, cooling to 30-60 degrees C, and obtaining solution containing 3,4-dichlorobenzene isocyanate and aromatic compounds solvent after eliminating undissolved substances and solvent in the feed liquid under vacuum degree of higher than - 0.098 MPa; and    (B) adding the obtained solution while stirring into a reaction unit, dropping 40% of dimethylamine aqueous solution, 3,4-dichlorobenzene isocyanate and dimethylamine at a ratio of 1:1-1.15, finishing dropping within 0.5-3 hours, raising temperature to 35-50 degrees C, reacting for 2-3 hours with pH value of 7-8, cooling to 0-10 degrees C, centrifugal filtering, rinsing filter cake using aromatic compounds solvent, recovering solvent, drying at 90-100 degrees C after washing the filter cake to neutral, and obtaining diuron, a molar ratio of 3,4-dichloroaniline to dimethylamine is 1:1-1.3.