The invention discloses a preparation method of an aluminum-based composite material. The preparation method comprises the following steps that after high-temperature sintering is performed on a mixture of SiO2, carbon fiber, expanded graphite powder and Al2O3, ball milling is carried out, Si is added, high-temperature sintering is carried out to coat or load the Si on the SiC surface by infiltration, secondary ball milling is carried out, aluminum powder and paraffin are added and pressed to obtain a plate, degreasing and sintering are performed on the plate, and multi-temperature-stage and multi-time densification pressing are performed to obtain the aluminum-based composite material. According to the preparation method, the composite material Si / SiC / Al achieves good interface bonding, and atom and molecule physicochemical property matching is good; and meanwhile, the problems of material deformation and the like caused by expansion coefficient difference are solved, the thermal expansion coefficient is low, the weight is light, the mechanical property is good, the heat conductivity, the strength, the plasticity, the heat dissipation property and other properties are good, the operation process is simple, the production control is facilitated, and the preparation method is simple in structure, low in cost, and liable to weld and industrially produced, and can be widely applied to the field of electronic packaging and has a good application prospect.