In this study, expanded graphite (EG)–calcium chloride composites were prepared, and their thermal storage and exothermic properties were studied. EG was obtained by heating expandable graphite (200 mesh, moisture 0·5%) in a muffle furnace at 340°C for 180 min. The EG–calcium chloride composite was prepared by mixing well and grinding an amount of calcium chloride hexahydrate (CaCl₂·6H₂O) with EG into powder in a mortar. The results show that parameters such as the proportion of EG, the dehydration temperature and the duration of dehydration of the composite affect the exothermic properties of the composite material distinctly, and the optimal exothermic performance of the composite is significantly better than that of pure calcium chloride. The exothermic value of the composite reaches the highest value of 1598·52 J/g at a mass ratio of calcium chloride to EG of 5:1 and a dehydrating temperature of 250°C for 2 h.