NOVELTY - A modified graphite preparing method involves utilizing oxidizing acid or salt to carry out oxidation treatment on natural graphite to obtain an intermediate product graphite A. The graphite A is centrifuged, washed and dried to obtain an immediate product graphite B. Polymer is dissolved into organic solvent to obtain a polymer solution. The graphite B is added into the polymer solution followed by stewing the mixture and evaporating to obtain graphite C. The graphite C is cured under protective atmosphere to obtain graphite D followed by carbonizing graphite D to obtain finished product.    USE - Method for preparing modified graphite that is utilized in a lithium ion secondary battery.    ADVANTAGE - The modified graphite has high charging and discharging efficiency and better cycle performances, and can be prepared in a simple, easy and cost-effective manner.    DETAILED DESCRIPTION - A modified graphite preparing method involves utilizing oxidizing acid or salt to carry out oxidation treatment on the natural graphite to obtain an intermediate product graphite A. The graphite A is centrifuged, washed and dried to obtain an immediate product graphite B. Polymer as a shell material is dissolved into an organic solvent at ratio of 1:10-5: 1 to obtain a polymer solution. The graphite B is added into the polymer solution and stirred in the mixture to uniformly soak the graphite B into the polymer solution followed by stewing the mixture, evaporating an organic solvent and sieving the mixture to obtain graphite C. The graphite C is cured at 100-600 degrees C for 0.2-12 hours under the protective atmosphere to obtain graphite D followed by carbonizing the graphite D at 700-1500 degrees C for 1-24 hours to obtain finished product, where oxidizing acid or salt is concentrated sulfuric acid, concentrated nitric acid, ammonium sulfate, hydrogen peroxide, strontium, shell layer material is epoxy resin, phenolic resin, polyacrylonitrile, polyvinyl alcohol, polystyrene, polyvinyl pyrrolidone and polyacrylic acid, and the organic solvent is PVC acetone, absolute ethyl alcohol, N,N-dimethyl formamide, benzene, toluene, chloroform and cyclohexane.