The invention relates to a method for synthesizing 4-chloro-2, 3, 5-tetramethylpiperidine by using a microreactor. According to the method, intermediate 2, 5-dimethoxychlorobenzene of 4-chloro-2, 5-dimethoxynitrobenzene and nitric acid are used as raw materials, 4-chloro-2, 5-dimethoxynitrobenzene is synthesized through the microreactor, in the reaction process, the mass fraction of nitric acid is50%-95%, and the mass fraction of a 2, 5-dimethoxychlorobenzene solution is 15%-50%; the feeding molar ratio of nitric acid to 2, 5-dimethoxychlorobenzene is (1.0-1.5): 1, the reaction temperature is50-85 DEG C, the feeding temperature is not higher than 50 DEG C, and the reaction retention time is 30-120 seconds. According to the method, on one hand, the process conditions such as the materialratio and the reaction temperature are accurately controlled, the dosage of nitric acid is reduced, the method is environmentally friendly, the conversion rate of 2, 5-dimethoxychlorobenzene reaches 99.98%, and the yield of 4-chloro-2, 5-dimethoxynitrobenzene reaches 99.5% or above; on the other hand, the key problems of corrosivity of nitric acid, difficulty in controlling the reaction temperature, poor mass and heat transfer effect, poor safety and the like in the conventional synthesis process are solved, and the reaction risk is low; strong operability.