Provided are a method of manufacturing a diamond-graphene hybrid heat spreader-thermal interface material assembled thermal management material including: (a) preparing a planar diamond base material; and (b) converting a predetermined thickness of at least a partial area of one side or both sides of the diamond base material into vertical graphene, wherein the diamond base material serves as a heat spreader, and a graphene layer formed on the diamond base material serves as a thermal interface material (TIM) or a heat sink, and a method of modulating the diamond-graphene hybrid thermal management material including modulating the thermal management material by attaching a heterogenous member to the surface of the diamond-graphene hybrid thermal management material and pressurizing the attached structure.