The invention discloses a preparation method for industrial-grade high-molecule-ratio cryolite, wherein the preparation method comprises the following operation steps: (1) taking a failure phosphate group polishing liquid, adding into a reactor, heating, at the same time, adding sodium fluoride, keeping the temperature at 45-70 DEG C, and carrying out a reaction for 30-50 min, wherein the molar ratio of fluorine in sodium fluoride to aluminum in the failure phosphate group polishing liquid is (1.0-1.4) to 1; and (2) after carrying out a reaction for 30-50 min in the step (1), allowing the obtained solution in the reactor to stand for 1-2 days, carrying out suction filtration of the substance obtained after standing, and drying the obtained precipitate to obtain the product. The method adopts the failure phosphate group polishing liquid as an aluminum source for carrying out reaction with sodium fluoride to obtain the industrial-grade high-molecule-ratio cryolite, the NaF/AlF3 value of the cryolite can reach 3.81, the product yield can reach 10%, and the yield is relatively high; and furthermore, the preparation method has the advantages of simple process, low cost and good application prospects.