The invention relates to the technical field of preparation of 2, 4-dinitroaniline, in particular to a method for preparing 2, 4-dinitroaniline by using a microreactor. The method comprises the following steps: (1) preparing equipment, namely preparing a preheater, the microreactor and two chromatographic pumps; (2) connecting reaction equipment, respectively connecting two chromatographic pumps with the preheater and the micro-reactor, then connecting the preheater with the micro-reactor, and putting the preheater and the microreactor into a constant-temperature oil bath after the connectionis completed; (3) conveying a reaction material, namely conveying ammonia water to the preheater at a preset flow rate, conveying the molten 2, 4-dinitrochlorobenzene to the microreactor at a preset flow rate, and mixing and reacting with the ammonia water to obtain 2, 4-dinitroaniline; and (4) after the reaction of the material in the step (3) is completed, preparing the redundant ammonia gas into ammonia water again for reuse through an ammonia gas recovery device, and continuing to reuse the ammonia generated by the reaction of ammonium chloride generated by the reaction and potassium hydroxide. Tthe method has the characteristics of high production efficiency, low energy consumption, economy, environmental protection, safety and reliability.