A method for synthesizing benzotriazole comprises acts of: preparing a first solvent comprising 2-(2-hydroxy-5-methylphenyl) benzotriazole, a basic agent and molecular sieves and a second solvent comprising 3-chloro-2-alkyl propylene; mixing the solvents; and heating the solvents. This method requires only one reaction vessel and produces few by-products, therefore is simpler and cheaper to produce. Furthermore, the molecular sieves are cheaper than catalysts in conventional reactions and may be recycled, giving even greater economic benefits.