NOVELTY - A lithium-rich manganese-based cathode material preparing method involves dissolving soluble nickel, manganese, cobalt salt with deionized water to obtain a metal ion mixture. The nickel manganese mixed solution and cobalt salt is prepared by adding alkali or alkali solution, aqueous ammonia and deionized water into a reaction kettle, stirring the mixture, filtering the precipitate, washing and drying to obtain a precursor, preparing cathode material by mixing precursor and lithium compound with nickel, manganese, lithium, cobalt, compacting and sintering powder to obtain a finished product.    USE - Method for preparing lithium-rich manganese-based cathode material that is utilized in lithium-ion battery, electric vehicles and communications.    ADVANTAGE - The method enables preparing cathode material in simple and cost-effective manner.    DETAILED DESCRIPTION - A lithium-rich manganese-based cathode material preparing method involves dissolving soluble nickel, manganese, cobalt salt in the mol ratio of ((x1-y1/2)/(x1+(2-x1)/3)):(((2-x1)/3-y1/2)/(x1+(2-x1)/3)):(y1/(x1+(2-x1)/3)) with deionized water to obtain 0.1-3 mol/l metal ion mixture solution. The mixed solution is prepared by adding 0.1-6 mol per l alkali or alkali solution, 0.05-3 mol per l aqueous ammonia and 20-30% deionized water into a reaction kettle to obtain nickel manganese mixed solution and cobalt salt, followed stirring the mixture by heating, controlling temperature and pH of reaction kettle, co-precipitating the mixture to obtain precipitated product, filtering the precipitate, washing and drying to obtain a precursor comprising nickel-cobalt-manganese-hydroxide (Ni((x-y/2)/(x+(2-x)/3))Co(y/(x+(2-x)/3))Mn(((2-x)/3-y/2)/(x+(2-x)/3))(OH)2), preparing obtained precursor and lithium compound by mixing uniformly nickel, manganese, lithium, cobalt in the mol ratio of ((1+(1-2x)/3)/(x+(2-x)/3)+z):1, where x1 is 0-0.5, y1 is 0-0.15, x is 0-0.5, y is 0-0.1, and z is 0-0.1, compacting the mixed powder and sintering the powder at high temperature to obtain lithium-rich manganese based cathode material.