Phase change material is one of the most promising materials in thermal energy storage systems. In this work, a new phase change composite of Stearic Acid@Multi-walled carbon nanotubes (SA@MWCNTs) is prepared by a simple vacuum absorption method. The as-prepared composite is determined by scanning electronic microscope (SEM), Fourier transformation infrared spectroscope (FT-IR) and X-ray diffractometer (XRD). The results show that outside diameters of the PCM composite are about 50-60 nm and Stearic Acid is encapsulated in the MWCNTs without chemical reaction. The DSC results indicate that the melting temperature and latent heat of the composite are 59.28 degrees C and 91.94 J g(-1), respectively. The encapsulation ratio of Stearic Acid is calculated to be 47% from the results of the DSC measurements. The as-prepared SA@MWCNTs composite was dispersed into the water to form stable suspension, and the suspension shows remarkable photo-thermal conversion performance with temperature increases from 30 to 80 degrees C. The receiver efficiency of this new kind of heat transfer fluid maintain 85% in wide temperature range. Furthermore, the PCM composite could maintain its phase transition perfectly after 50 melting-freezing cycles, and no leakage of paraffin was observed by SEM. The high heat storage capability and excellent photo-thermal conversion performance of the composite enable it to be a potential material to store solar energy in practical applications.