The invention discloses a method for preparing a high-strength heat preservation building block from graphite tailings, and relates to the technical field of composite materials; according to the process method, graphite tailings, cement and kaolin are used as main raw materials; the graphite tailings are deeply pretreated, magnetic components and active metal oxides in the graphite tailings are removed, and the graphite tailings are subjected to expansion treatment, so that the specific surface area of the graphite tailings is increased, the strength of the thermal insulation building block is improved, the density of the thermal insulation building block is reduced, and the dead weight of the thermal insulation building block is reduced.