A graphene-reinforced alloy composite material and a preparation method thereof are disclosed. The method includes preparing a porous graphene colloid, smelting a first-part alloy, pouring it into the porous graphene colloid to be formed, subjecting the formed product to a hot extrusion, and pulverizing into a powder I; smelting a second-part alloy into an alloy melt II, adding a high-purity silicon powder therein, mixing by stirring, and atomizing to obtain a powder II; mixing the powder I and the powder II, to obtain a pretreated alloy powder; placing the pretreated alloy powder in a high-purity ark, transferring the high-purity ark to a high-temperature tubular furnace, subjecting the pretreated alloy powder to a redox treatment, and introducing methane and hydrogen to grow graphene, to obtain a coated alloy powder; subjecting the coated alloy powder to a pre-compressing molding and sintering, to obtain the graphene-reinforced alloy composite material.