The invention discloses a method for preparing a carbon-silicon negative electrode material of a lithium ion battery through in-situ compositing, and the method comprises the following steps: taking graphene oxide as a carbon source, and mechanically stirring the graphene oxide and silicon nanoparticles to obtain a suspension; adding ascorbic acid into the suspension, performing uniform stirring,and heating the mixture to 50-80 DEG C; reducing the graphene oxide by ascorbic acid, separating out the graphene oxide and the silicon nanoparticles coating the graphene oxide, performing washing with water, and performing drying to obtain a product. The silicon nanoparticle and graphene compounded negative electrode material disclosed by the invention can overcome the defect of serious volume expansion of a silicon-based negative electrode material; the excellent electrical, thermal and mesoscopic structure characteristics of the graphene can be brought into play; while the high energy density is achieved, the good charge-discharge performance and cycle performance are achieved, so the graphene-based negative electrode material of the lithium ion battery becomes the negative electrode key material of a next generation lithium ion battery. Meanwhile, the graphene oxide has good water solubility, an aqueous solution system and a reducing agent in the preparation process are non-toxic and harmless, the cost is low, the energy consumption in the whole reduction process is low, and the reaction post-treatment procedure is simple.