A self-assembly method is introduced to prepare composite phase change materials (PCMs) consisting of 1-octadecanol (OD) and graphene. The shape stability and thermal properties of 1-octadecanol/graphene composite PCMs with three-dimensional network structure are investigated. Graphene Is dispersed evenly in OD matrix and the three-dimensional network structure is getting tighter with increasing ratio of graphene. OD is completely encapsulated at relatively low amount of graphene about 1.5 wt%. XRD and Raman results show that the combination between OD and graphene is physical adsorption. The 1-octadecanol/graphene (OG) composite phase change materials possess excellent shape stability, which can prevent the leakage of molten OD during phase transition. In addition, around 99.3% phase change enthalpy of pure OD is maintained by connected network structure of graphene while the melting and solidifying temperature merely have small fluctuations. The thermal conductivity of composite phase change material with 1.5 wt% graphene increases to 0.358 W/ (m K), which is 1.5 times higher than that of pure OD. Furthermore, the porous network of graphene can delay the evaporation and thermal decomposition point of the composite phase change materials, thus extending the operating temperature of OD efficiently. This work provides a promising way to encapsulate low-temperature organic phase change materials with little carbon additives, and enhance the thermophysical properties of base materials simultaneously.