The invention discloses a silicon-carbon composite anode material for a lithium ion battery and a preparation method thereof. The preparation method comprises the steps that: a nano silicon/graphite dispersion liquid is prepared by using nano silicon, a coupling agent and graphite, and then a porous carbon source is added for drying and carbonization to obtain a precursor 1, then the precursor 1 is mixed with an organic cracking carbon source for dynamic coating and carbonization to obtain a silicon carbon composite material. The silicon-carbon composite anode material forms a multilayer structure from the inside to the outside, wherein the inner layer is a plurality of composite particles formed of nano silicon and graphite fine powder; the intermediate layer is a first buffer layer having a porous structure formed by carbonization of a porous carbon material; and the outer layer is a second buffer layer of the organic cracked carbon coating the outer portion of the intermediate layer. The preparation method is simple, and the obtained material has the excellent first efficiency and the excellent cycle performance.