The invention discloses a method for continuously synthesizing a benzotriazole ultraviolet absorber. The method comprises the following steps of charging a reduction solid catalyst into a fixed bed reactor; dissolving a compound represented by the formula (I) and an alkali in a solvent to prepare a 1%-35% solution of the compound represented by the formula (I), continuously introducing the solution into the fixed bed reactor at the volume space velocity of 0.015-300h<-1>, introducing hydrogen and heating so that the pressure of hydrogen in the fixed bed reactor is 0.1-10MPa and the temperature is 40-220 DEG C; continuously flowing a reaction liquid out from the lower end of the fixed bed reactor, cooling the effluent reaction liquid, carrying out gas-liquid separation, filtering the liquid, evaporating the filtrate to remove the solvent and purifying to obtain the benzotriazole ultraviolet absorber represented by the formula (II). The method is simple in process, environmental friendly, inexpensive in cost, high in yield of the product and is suitable for industrial production. The reduction solid catalyst used in the method is stable in activity and long in service life.