The invention discloses a building heat-preservation and fireproof composite material and a preparation method thereof. The composite material is characterized by comprising the following raw materials in parts by weight: 20-35 parts of slag wool, 10-20 parts of a sepiolite powder and 10-15 parts of an ash calcium powder, 1-5 parts of hydroxypropyl methylcellulose, 10-15 parts of bamboo fibers, 6-15 parts of an aluminum powder, 1-3 parts of an instant rubber powder II, 3-8 parts of a foaming agent, 2-6 parts of a water-proofing agent, and 10-25 parts of sawdust. The heat-preservation and fireproof composite material provided by the invention is suitable for being applied to heat insulation, heat preservation, energy conservation and decoration for inner wall surfaces of various buildings.