The reduced-graphene oxide aerogel was prepared by the colloidal agglomeration method. Using graphene oxide (GO) as the raw material, the reduced graphene oxide aerogel/eicosane composite phase change material was obtained through self-diffusion eicosane (Eicosane). Finally, the relationship between composite materials and performance was explored. Thermogravimetric (TGA) and differential calorimetry scanners (DSC) were used to test the thermal properties of eicosane and composite materials, the relationship between the mass fraction of eicosane and the enthalpy of the composite material was confirmed, and the influence of the phase change cycle on the materials stability was further explored. The results showed that the enthalpy of the composite was directly proportional to the mass fraction of eicosane. After 50 phase change cycles, PCM4 remains stable. The thermal conductivity analysis displayed that reduced graphene oxide aerogel could improve the thermal conductivity of the eicosane. In addition, through the sunlight simulation test, it is calculated that the light-to-thermal conversion efficiency of the composite material is about 55%.