The invention discloses a preparation method of a lithium manganese ferric phosphate anode material. The method comprises the steps of uniformly mixing a lithium hydroxide solution and a phosphoric acid solution, adding a carbon source and a surfactant to prepare a solution A, uniformly mixing a ferrous salt solution and a manganous salt solution to prepare a solution B, dropwise adding the solution B to the solution A to form a suspension C, shifting the suspension C to a magnetic stirring hydrothermal kettle to obtain precursor slurry of in-situ carbon coated lithium manganese ferric phosphate, quenching the precursor slurry with cooling water to a room temperature, performing filtering, sufficiently washing a filtered filter cake with an aqueous solution for 3-5 times, and placing the washed filter cake in a vacuum drying oven to finally obtain the in-situ carbon coated lithium manganese ferric phosphate anode material. The anode material prepared by the method has the characteristics of uniform carbon coating layer thickness, uniform nano particle size distribution, good cycling stability, excellent rate capability and the like.