A method for producing high-molecular ratio cryolite by utilizing low-concentration fluosilicic acid comprises the following steps: (1) synthesizing an aluminum fluoride solvent: heating the fluosilicic acid of which the concentration is 13 to 14 percent to be 65 DEG C to 75 DEG C through a heat exchanger, and performing reaction between aluminum hydroxide and the fluosilicic acid for 12 to 16 minutes at 70 to 80 DEG C under stirring; after the reaction is ended, flushing a residual product in a reaction tank with water, merging the residual product with a reaction product, filtering, then, washing a filter cake with water, and merging washing liquid with reaction filtrate to obtain the aluminum fluoride solvent; (2) synthesizing the cryolite: performing reaction between the prepared aluminum fluoride solvent and sodium fluoride in stoichiometric ratio of (1:2.8) to (1:3.2) under 80 to 90 DEG C for 50 to 60 minutes under stirring, filtering a reactant after the reaction is ended, delivering filtrate into a sewage pool for disposal, performing flash drying on a filter cake under controlled temperature of 120 to 150 DEG C to obtain the high-molecular ratio cryolite. The high-molecular ratio cryolite synthesized by the method disclosed by the invention is high in quality as well as yield; moreover, volume of sewage generated by the method is low, and the sewage is easy to dispose.