Na₃PO₄ as a chemical thermal storage material has the advantages of low thermal storage temperature, high thermal storage density and low price, and has good prospects for lowtemperature solar thermal storage applications, but the problem of easy deliquescence of the pure material limits its application. In this paper, activated carbon based Na₃PO₄ (R-AC@Na₃PO₄) composites with loadings (mass fraction w) of 0.3, 0.5 and 0.8 were prepared using activated carbon as the porous matrix, and their morphological and structural characterization and thermal storage properties were investigated. The results show that the addition of activated carbon can significantly increase the hydration rate of the composites at an ambient temperature of 30^◦C and a relative humidity of 60%, and the time to reach hydration equilibrium is only 30%, 35%, and 40% of that of the pure material at Na₃PO₄ loadings of 0.3, 0.5, and 0.8; the heat storage density of the composites increases with the increase of the loading, and at 0.8 loading, the maximum heat storage density of 675 J·g⁻¹ can be reached, which is 70% of that of the pure material. The study provides a certain reference for the development of low-temperature chemical heat storage materials.