The invention relates to a method for preparing foam glass by boron sludge fly ash, relating to the preparation filed of the glass in the non-metallic inorganic material and taking the boron sludge and the fly ash as raw materials; wherein MgO is introduced by the boron sludge, and SiO2, Al2O3, and CaO are introduced by the fly ash; the method for preparing the foam glass by boron sludge fly ash is characterized in that the method comprises steps: the boron sludge, the fly ash, Na2CO3 or NaSiF6, sodium phosphate or boric acid are weighted together according to the prescription, and then are packed into a ball mill for ball milling to the fineness of technological design; after being dried, the mixture is pelleted by a dry method, and shaped products are packed into a resistance furnace forheating after pressure forming and drying; after the constant temperature, the power source is turned off till the shaped products are naturally cooled to the room temperature, afterwards, cold working is carried out till the needed CaO-MgO-Al2O3-SiO2 series foam glass. The method effectively and reasonably uses waste natural resource, reduces environment pollution, has simple technique, low costand wide market prospect.