The invention discloses a preparation method for a low-cost graphene-modified negative electrode material. The preparation method comprises the following steps of dispersing graphene powder in a solvent, preparing a graphene aqueous dispersion liquid or ethyl alcohol dispersion liquid, adding silicon powder, and continuing to disperse to obtain a mixed liquid; transferring the mixed liquid to a hydrothermal reaction kettle with a temperature being 150-250 DEG C for reaction for 10-14 hours; taking a material out for drying after reaction is completed, and performing smashing, grinding and sieving to obtain a mixture A; adding the mixture A, graphite and an additive into a supercritical fluid, and performing uniform stirring to obtain a mixture B; and performing spray drying on the obtainedmixture B, and performing collection to obtain powder. By employing petroleum coke, the material cost is effectively controlled, pore forming is performed on a surface coated with the petroleum coke,a honeycomb structure with rich holes is formed, so that the specific surface area and the liquid absorption and maintenance capability of the graphene composite negative electrode can be substantially improved, and the structure stability and the cycle property of the graphene composite negative electrode are improved.