NOVELTY - A lithium ion battery cathode material preparing method involves weighing lithium compounds, phosphorus compound, dispersing in a solvent, to prepare solution, adding additive, filtering, washing, and drying. Lithium, phosphate manganese source compound is dispersed in a solvent to obtain suspension after adding additive, solution is sealed in system, performing solvothermal reaction, washing, and drying to give pure phase of lithium manganese phosphate, followed by dispersing lithium manganese phosphate compound with carbon source in solvent, stirring, performing heat treatment, and cooling.    USE - Method for preparing lithium ion battery cathode material.    ADVANTAGE - The material has porous hollow structure, improved electrochemical performance, cycling stability, low energy consumption and easy process to control, in favor of industrial production.    DETAILED DESCRIPTION - A lithium ion battery cathode material preparing method involves weighing lithium compounds, phosphorus compound, dispersing in a solvent, to prepare 0.1-1.5mol / L solution, mixing solutions for double a volume at a volume ratio of 1: 1, after the mass fraction of the mixture, adding 0-1% additive to adjust the pH value of 8-12, after the reaction for 10-60 minutes, filtering, washing, and drying to obtain lithium phosphate precursor. Lithium, phosphate manganese source compound is dispersed in a solvent at a molar ratio of 1: 1, to obtain 0.1-0.4 mol/L suspension after adding 0-10% additive, solution is sealed in the reactor system, at 140-240 degrees C, performing solvothermal reaction for 3-24 hours, washing, and drying to give pure phase of lithium manganese phosphate, followed by dispersing lithium manganese phosphate compound with an organic carbon source at mass ratio of 2-5: 1 in a solvent, stirring, evaporating to dryness naturally, performing heat treatment on the mixture under an inert atmosphere, cooling at room temperature, to obtain a lithium manganese phosphate - carbon composite.