Eutectic mixture of binary organic composite of capric acid（CA） and hexadecanol（H） was synthesized by the ultrasonic method. The binary organic eutectic mixture（CA H）/expanded graphite（EG） composite with various mass fraction of CA H（50%, 60%, 80%, 90%）as a composite phase change material（PCM） was prepared by vacuum absorption technique using CA H as phase change material and EG as carrier. The thermal properties and structure of the composite material were characterized with the help of XRD, FTIR, SEM and DSC. The result shows that the melting temperatures and the latent heats of CA H/EG PCM with 80% of CA H are measured to be 22.4℃ and 93.87J/g by DSC analysis.