The invention discloses a method for preparing an Invokana medicine intermediate by using a micro-reactor, which is characterized in that a compound III dissolved in an organic solvent and an organometallic reagent respectively passes through a material channel and are mixed in a micro-reactor unit (L), and passes through (L) and flow to the micro-reactor unit (H); a compound II dissolved in the organic solvent passes through the material channel and then is mixed with the above mixed liquor in the micro-reactor unit (H) at preset temperature, then a mixture passes through the micro-reactor unit (H), flow out from an outlet after a reaction is completed, a reaction solution is subjected to post treatment to obtain the target compound-Invokana medicine intermediate I. According to the invention, the Invokana medicine intermediate (I) is synthesized by the micro-reactor, so that heat transfer problem of the reactions can be effectively solved, the reaction objects in the micro-reactor can be fully mixed, reaction time is shortened, reaction efficiency is increased, almost no amplification effect is generated on the micro-reactor, the method has high safety performance, and is suitable for industrial production.