Abstract: In order to explore the ways and mechanisms to improve the thermophysical properties of paraffin-based phase change materials, Cu nano-surface-amorphous n-octadecane composite system and Cu nano-surface-graphene/n-octadecane composite system were established by introducing Cu nano-surface. And molecular dynamics simulation method was used to simulate and analyze the two composite systems. The results show that the microscopic mechanism of adding metal nanoparticles to the system to improve the thermophysical properties of phase change materials lies in not only its very high thermal conductivity, but also the interaction between the metal nano surface and the alkane molecule promoting the alkane molecule on the nano-surface directional crystallization. Graphene, as a high thermal conductivity carbon nanomaterial with excellent performance, can further promote the oriented crystallization of alkane molecules in the composite system, thereby improving the thermal conductivity of the composite phase change material in the entire system.