The invention provides a building heat preservation material, which consists of the following materials in weight percentage: 18 to 25 percent of expanded perlite, 10 to 15 percent of cinder, 37 to 42percent of magnesia, 3 to 5 percent of calcium carbonate, 8 to 12 percent of coal ash and 14 to 18 percent of binding agent. The preparation method of the building heat preservation material comprises: the expanded perlite, the cinder, the magnesia, the calcium carbonate and the coal ash are crushed and screened by a 200 to 300 mesh sieve; the expanded perlite, the cinder, the magnesia, the calcium carbonate, the coal ash and the binding agent are weighed up according to the weight percentages and evenly mixed, added with water and stirred to be pasty, poured in a mould with a film at the bottom for forming, cured in the mould for 10 to 36 hours and demoulded. The building heat preservation material has the advantages of high strength, pressure resistance, good shock resistance and long service life.