Abstract: Presently, combining porous and high-thermal-conductivity matrices with phase change materials is widely used to improve the comprehensive properties of organic composite phase change materials. Porous carbon, as a carrier material with strong load capacity and good thermal conductivity, has become a focus of interest in research. Nevertheless, how to easily prepare this material in a green and inexpensive way still remains a challenge. Subsequent to heat treatment at gradient temperature and nitrogen atmosphere, the biomass materials were carbonized and further transformed to graphite. Then, the porous high-thermal-conductivity carbon materials were obtained by replicating the structure of biomass natural materials. Finally, the biomass porous carbon/paraffin composite phase change materials were prepared using vacuum melting impregnation method. The obtained biomass porous carbon and composite phase change materials were characterized by scanning electron microscope (SEM), flourier transformation infrared spectroscopy (FTIR), thermal gravity analysis (TGA), X-ray diffractometer (XRD), Raman spectroscopy, mercury intrusion porosimetry (MIP), differential scanning calorimetry (DSC), and hot-disk thermal analysis. The characterization results show that the structure of the biomass porous carbon material is well preserved, which ensures the efficient and stable load of organic phase change materials. In terms of heat transfer efficiency as compared with pure paraffin materials, the thermal conductivities of porous pine carbon and bamboo carbon/paraffin composite phase change materials are increased by 100% and 216%, respectively, reaching 0.48 W·m^‒1·K^‒1 and 0.76 W·m^‒1·K^‒1, respectively. Based on these results, by comparing the loading amount of paraffin, phase change enthalpy, and thermal conductivity of the composite phase change materials prepared from pine and bamboo, the influence mechanism of the biomass structure on the properties of the composite phase change materials is further explored. In summary, unlike the traditional composite phase change materials, the preparation process in this experiment is simple, the raw material sources are widely available, cheap, and green, and the thermal conductivity is significantly improved. Therefore, the proposed preparation process has a broad application prospect in the future.