The invention relates to a method for preparing highly pure hydrazinobenzene by using continuous flow micro-channel reactor. The method concretely comprises the following steps: preparing aniline hydrochloride from hydrochloric acid and aniline, respectively pumping the aniline hydrochloride and a sodium nitrite solution into the micro-channel reactor by two metering pumps to obtain a diazo salt solution, reducing the obtained reaction solution, carrying out acid separation on the reduced solution, filtering the obtained solution, neutralizing the filtered solution, and distilling the neutralized solution to obtain the highly pure hydrazinobenzene. The diazotization process is a strong exothermic reaction, and the generated diazo salt easily decomposes after standing at a high temperature for a long time, and generates toxic gases which pollute environment and even blast. The mixing effect of the heart-shaped micro-channel reactor is far better than the mass transfer effect generated by stirring, so the aniline conversion rate can reach 99%, the mixing mass transfer effect is good, and heat conduction is fast to avoid local overheating phenomenon; and the reaction can be carried out at constant temperature conditions, so the temperature runaway blast danger of general reactors is eliminated, and the safety is improved.