The invention discloses a method for synthesizing acyl naphthalene by using a micro-channel reactor. The method comprises the following steps: (1) preparing acylation liquid, namely adding nitrobenzene and anhydrous aluminum chloride into a reactor in a low-temperature tank, finally adding acyl chloride, and controlling the temperature in the reactor to be 0-3 DEG C; (2) preparing a feed solution,namely adding nitrobenzene and 2-methyl naphthalene into a reactor provided with a stirrer; (3) reacting, namely injecting the feed solution and the acylation liquid into a micro mixer to be mixed, and feeding into the micro-channel reactor to be reacted; (4) washing, namely enabling the product discharged from the micro-channel reactor to enter the micro mixer again so as to be washed, enablingthe mixture into the micro-channel reactor, controlling the reactor temperature to 40-50 DEG C, and performing ultrasonic oscillation outside the reactor; (5) performing reduced pressure distillation,namely separating the products obtained in the step (4), and performing vacuum decompression to 500-1000Pa so as to obtain a crude product 2-methyl-6-acyl naphthalene; and (6) recrystallizing, namelyadding the crude product obtained in the step (5) into a solvent of 50-60 DEG C, stirring and dissolving, naturally cooling and crystallizing, continuously cooling and crystallizing in an ice-water bath, and finally filtering to obtain the purified product 2-methyl-6-acyl naphthalene.