The invention discloses a polysilicate/NCM three-component composite positive electrode material for a lithium ion battery and a preparation method thereof. The three-component composite positive electrode material is prepared by compounding polysilicate and an NCM three-component positive electrode material, wherein the mass content of polysilicate is 0.1 to 10.0% while the mass content of the NCM three-component positive electrode material 90 to 99.9%. The preparation method comprises the following steps: uniformly dispersing ethyl orthosilicate or a derivative thereof in an organic solvent; then subjecting a solution obtained in a previous step and the NCM three-component positive electrode material to ball milling mixing; and allowing ethyl orthosilicate or the derivative thereof to directly undergo condensation polymerization on the surface of NCM under the catalysis of NCM surface alkali so as to obtain the polysilicate/NCM three-component composite positive electrode material. The coating of the composite material can react with HF in an electrolyte, so the purpose of protecting an active material is achieved.