The invention relates to a heat storage material and a preparation method thereof, wherein the heat storage material comprises, by weight, 55-60 parts of an eutectic salt, 10-15 parts of inorganic clay, 15-20 parts of nanometer magnesium oxide and 5-20 parts of magnesium oxide. According to the invention, the heat storage material is reasonable in component, good in stability and high in working temperature, and cannot generate problems of molten salt volatilization and molten salt leakage.