NOVELTY - Preparing lithium ferric phosphate (LiFePO4) cathode active material comprises: heating an anode scrap; separating and collecting the cathode active material; heat-treating the material; changing a structure of the material, and precipitating the ferric phosphate (FePO4); obtaining and filtering the FePO4 solid content; obtaining the crystalline ferrous pyrophosphate solution (Fe2P2O7), and heat-treating; and preparing the LiFePO4 cathode active material by heat-treating the solution after doing the mixing with lithium compound under the reducing atmosphere or the inert atmosphere.    USE - The method is useful for preparing LiFePO4 cathode active material useful in an anode of a lithium secondary battery (all claimed) of a small-sized electronic product e.g. electronic device, handheld computer or cellular phone, and large capacity lithium secondary batteries for an electric vehicle.    ADVANTAGE - The LiFePO4 cathode active material is prepared in a simple, economical and environment-friendly manner.    DETAILED DESCRIPTION - Preparing lithium ferric phosphate (LiFePO4) cathode active material comprises: heating an anode scrap including a LiFePO4 cathode active material under the nitrogen atmosphere; separating the LiFePO4 cathode active material from the anode scrap, and collecting the LiFePO4 cathode active material; heat-treating the LiFePO4 cathode active material under the air atmosphere; changing a structure of the LiFePO4 cathode active material by dissolving the cathode active material in an acid solution by adding an ammonia solution, and precipitating the ferric phosphate (FePO4); obtaining the FePO4 solid content, and filtering the solid content; obtaining the crystalline ferrous pyrophosphate solution (Fe2P2O7), and heat-treating under the hydrogen atmosphere; and preparing the LiFePO4 cathode active material by heat-treating the crystalline ferrous pyrophosphate solution after doing the mixing with lithium compound under the reducing atmosphere, carbon source or the inert atmosphere.