The present invention discloses a method for producing cryolite by using fluorine-containing slag of electrolytic aluminum. The method comprises the following steps: (1) smashing fluorine-containing slag of electrolytic aluminum to 180-350 mesh, and then performing flotation to obtain coarse cryolite containing 5-10% of carbon in mass percent; (2) putting the coarse cryolite in a reaction kettle, adding water in the reaction kettle with the mass of water being 5-15 times of that of the coarse cryolite, and stirring to be uniform; (3) continuing stirring, adding acid mixed solution in the reaction kettle with the mass of the acid mixed solution being 1/5-1/2 of that of the coarse cryolite, heating to 50-100 DEG C, stirring for 0.5-1 hour and stopping stirring; and (4) after stopping stirring, separating the slurry in the reaction kettle by a centrifugal machine to obtain solid, and drying the solid to obtain the product cryolite, returning the mother liquor to step (3) for recycling, and after2-3 times of recycling, returning to step (2) for use. The product cryolite produced by the invention is white in color and qualified in quality, and satisfies cryolite national standard requirement.