A photo-thermal energy storage microcapsule modified by KH550-treated ZrC nanoparticles was prepared via in situ polymerization. ZrC nanoparticles were treated by KH550 to stabilize the paraffin-ZrC emulsion, which could ensure ZrC nanoparticles were incorporated into the microcapsule shell. In this article, microcapsules modified by different mass fractions of modified ZrC nanoparticles (paraffin@MUF-ZrC) were prepared to investigate the influence of ZrC nanoparticles on microstructure, thermal storage, thermal stability, thermal conductivity, and photo-thermal conversion behavior. According to the SEM images, the obtained paraffin@MUF-ZrC microcapsules exhibited good morphology with regular spherical shape and uniform particle size distribution. DSC, TGA, and thermal conductivity analysis were used to characterize the thermal storage properties, thermal stability, and thermal conductivity of paraffin@MUF-ZrC microcapsules, respectively. It showed that these three thermal performance indices improved as the mass fraction of modified ZrC nanoparticles increased. Specifically, the thermal properties of paraffin@MUF-4%ZrC microcapsules were better than paraffin@MUF microcapsules. As a result, specific enthalpy was slightly increased by 14.92% (121.74 J/g) and thermal conductivity increased by 225.16% (0.4962 W/m center dot K). Moreover, the optical absorption capability also increased. The paraffin@MUF-4%ZrC microcapsules showed remarkable optical absorption capability of 70.23%, which was a 247.67% improvement compared to the 20.20% of the paraffin@MUF microcapsules. Moreover, it was found that paraffin@MUF-4%ZrC microcapsules could heat up from 30 degrees C to 78 degrees C under simulated solar radiation, showing excellent photo-thermal conversion behavior. Based on good thermal storage properties, thermal conductivity, and light absorption capability over the full spectrum, the new photo-thermal energy storage microcapsules have good application prospects in solar thermal conversion and energy storage systems.