In this study, CNT-BN-SA-1 composites were prepared by vacuum impregnation using stearic acid (SA) as a phase change material (PCM), multi-walled carbon nanotubes (CNT) and hexagonal boron nitride (BN) as support materials. According to the results of the thermal conductivity of CNT-BN-SA-1, the maximum thermal conductivity of CNT-BN-SA-1 is 0.83 W m K⁻¹ when the CNT-BN content reaches 15 wt%. The surface morphology, heat storage capacity, and reliability of CNT-BN-SA-1 were systematically studied. The melting temperature (ΔT_m) of CNT-BN-SA-1 is 51.83 °C and the latent calorific value is 143.5 ± 5.0 J g⁻¹. CNT-BN-SA-1 still exhibits good latent heat capacity after 1000 heat treatment cycles, and its latent heat after cycling is 147.3 ± 5.0 J g⁻¹. After a high temperature of 100 °C, CNT-BN-SA-1 still retains a good solid shape. The results show that CNT-BN-SA-1 has high latent heat, reliability, and excellent CSP energy storage capabilities. It has great application potential in the field of FSPCMs. This method provides a certain reference for the preparation of phase change composites.