As heat storage and heat transfer medium, molten salt plays a vital role in achieving high heat transfer efficiency in concentrating solar power (CSP) plants. In this study, ternary chloride salts (NaCl–KCl–MgCl 2 ) is considered as the base salt and the nanocomposites doped with different mass fractions of CuO are synthesized using the solution evaporation method. The thermophysical properties of the nanocomposites, including melting temperature, phase change enthalpy, specific heat, thermal diffusivity, and thermal conductivity are investigated. The experimental results indicated the melting temperature of the nanocomposites is very close to that of the base salt. The specific heat of the nanocomposite in the liquid phase region is 10.51% higher than that of the base salt when the mass fraction of CuO was 0.7%. The addition of CuO nanoparticles significantly increase the thermal diffusivity and thermal conductivity of the base salt. The thermal diffusivity and thermal conductivity of the nanocomposites are increased by 10.95–37.23% and 15.85–39.55% compared to the base salt, respectively. The nanocomposites doped with CuO nanoparticles exhibit good application prospects and excellent thermal energy storage performance for high-temperature CSP systems. To improve the heat transfer characteristics of chloride salts, nanocomposites doped with 0.2, 0.7, and 2.0 wt% CuO nanoparticles were synthesized. The nanocomposites showed excellent TES performance for high-temperature CSP systems. • Nanocomposites doped with CuO exhibited excellent thermal energy storage performance. • Specific heat in liquid phase region had an enhancement of 10.51% by doping 0.7 wt% CuO nanoparticles. • Thermal diffusivity of nanocomposites increased with increasing temperature. • Thermal diffusivity and thermal conductivity of base salt can be increased by adding CuO nanoparticles. • The mechanism of the enhancement of thermophysical properties of nanocomposites was investigated.