The invention provides a method for preparing a lightweight refractory material from waste mullite-corundum bricks, and belongs to the technical field of refractory materials. The method comprises the following steps: selecting waste mullite-corundum bricks, roughly crushing, performing magnetic separation to remove iron, crushing into a granular material of which the particle size is smaller than 1 mm, performing chemical analysis on the fine granular material; adding calcium carbonate and a poring agent into a waste mullite brick fine granular material so as to prepare a mixed material, adding a molding agent, and ball-milling so as to prepare slurry; finally, performing cementing molding, drying, and high-temperature sintering, thereby obtaining the lightweight refractory material. The lightweight refractory material prepared by the method takes mullite as main crystal phase and anorthite as secondary crystal phase, and the product is high in porosity and small in volume density and is a lightweight refractory material. Not only are waste refractory materials effectively utilized, but also a preparation method which is relatively low in cost and simple in process is provided, environmental pollution is reduced, and the prepared lightweight refractory material can be widely applied to heat preservation and thermal insulation.