NOVELTY - Preparation of 2,4-dichlorophenoxyacetic acid involves adding sodium hydroxide solution to a reactor and then stirring, adding phenol and sodium bicarbonate to the reactor, uniformly mixing, heating the mixture at 100 degrees C for 40 minutes, adding hydrochloric acid to the mixture and then cooling, adding chloroacetic acid and water to the mixture and then mixing, adding nickel-aluminum-magnesium composite oxide to the mixture, stirring the mixture for 20-40 minutes and then reacting, cooling and filtering the mixture, and drying.    USE - The method is useful for preparation of 2,4-dichlorophenoxyacetic acid (claimed).    ADVANTAGE - The method enables simple and economical preparation of 2,4-dichlorophenoxyacetic acid with high yield, quality and purity, and excellent stability in an environmentally-friendly manner.    DETAILED DESCRIPTION - Preparation of 2,4-dichlorophenoxyacetic acid involves adding sodium hydroxide solution to a reactor and then stirring for 15-20 minutes, adding phenol and sodium bicarbonate to the reactor, uniformly mixing, regulating pH value to 11, heating the mixture at 100 degrees C for 40 minutes, adding hydrochloric acid to the heated mixture, adjusting pH value to 4, cooling the mixture using an ice water bath to obtain phenoxyacetic acid, adding chloroacetic acid and water to phenoxyacetic acid and then mixing, adding 0.05% nickel-aluminum-magnesium composite oxide to the mixture, stirring the mixture for 20-40 minutes, reacting the stirred mixture to obtain a reaction product, cooling and filtering the reaction product to obtain a solid mixture, and drying. Nickel-aluminum-magnesium composite oxide is prepared by adding nickel nitrate and magnesium nitrate to aluminum nitrate, uniformly mixing to obtain a mixed liquid, heating the mixed liquid at 50 degrees C, adding sodium bicarbonate to the heated liquid and then stirring at 50 degrees C to obtain a precipitate, performing hydrothermal reaction, crystallizing mixture and drying at 50 degrees C for 6 hours under vacuum. Nickel nitrate, magnesium nitrate and sodium bicarbonate are present in a mass ratio of 1:0.5:0.2:0.3.