The invention discloses a red-mud-fly-ash high-strength heat-preservation building block based on alkali excitation. Industrial waste fly ash and red mud serve as main raw materials, cement and quicklime serve as auxiliary materials, and fly-ash pottery sand or shale pottery sand serve as heat-preservation materials. The building block is prepared from, by mass, 18-40% of red mud, 18-30% of fly ash, 25-40% of pottery sand, 3-8% of cement, 3-10% of lime, 1-3% of straw fibers and 0.5-2% of early strength agents, the water content is 10-15%, aging is conducted for 8-36 hours, and molding is conducted under the pressure of 40 MPa; the building block is prepared by the steps of drying, grinding, weighing, mixing of the auxiliary materials, compression molding, standard maintenance and natural curing. The red-mud-fly-ash high-strength heat-preservation building block based on the alkali excitation has the advantages of being simple in molding process, capable of having a reaction and being cured quickly at room temperature, and free from sintering and stream-pressure, products of the building block are high in compressive strength and anti-dry-shrinkage performance and good in impermeability, and can be stored for a long time without scumming phenomena. A large amount of industrial waste can be utilized, the energy and resources are saved, and the cost and energy consumption are low.