The invention relates to a method for preparing foamed glass by using waste fiberglass products, which comprises the following steps of: firstly, airing collected waste fiberglass mats and fiberglass meshes, manually sorting out the impurities of metal, organic matter and the like, cutting into fragments smaller than 20 mm*20 mm, and ball-milling to 200 meshes to form glass powder; loading the glass powder, silicon carbide, diantimony trioxide, sodium sulfate, sodium fluoaluminate, sodium nitrate and cobalt oxide into a ball mill, and ball-milling to form a batch; loading the batch into a heat-resisting mold, and firing into foam glass. In the invention, the waste fiberglass products are used as a main raw material to produce foam glass, and the prepared foam glass has low density, high strength, small heat conductivity and low water absorption rate. The preparation method has simple operation process, low founding temperature and low cost, not only changes wastes into valuables, but also protects the environment, and is applicable to industrial production.