The invention discloses a method for recycling phosphorus and fluorine in phosphoric acid concentrated sludge acid and producing a low-fluorine water-soluble fertilizer through cogeneration. The method comprises the following steps: putting process water, potassium sulfate/potassium carbonate, active kieselguhr and concentrated sulfuric acid into phosphoric acid concentrated sludge acid, removing free fluorine in the sludge acid, converting semi-hydrated gypsum in the sludge acid into dihydrate gypsum to release inter-crystal phosphorus, and performing filtering separation so as to obtain a water phase, namely low-fluorine phosphoric acid; and enabling solid phase filter cakes to react with the concentrated sulfuric acid to decompose fluosilicate, performing water washing on a gas phase so as to obtain fluosilicic acid, pulping a reaction material with water, performing filtering separation, and neutralizing the liquid phase with liquid ammonia/ammonium hydroxide, thereby obtaining a mixed water-soluble fertilizer of oligomerization APP (Ammonium Polyphosphate), ammonium sulfate and potassium sulfate, and a solid phase, namely anhydrite. By adopting the method, recycling and reuse of phosphoric acid and fluosilicic acid in phosphoric acid concentrated sludge acid are achieved, the low-fluorine water-soluble fertilizer is produced through cogeneration, efficient utilization of phosphorus and potassium is achieved, and the difficulties that phosphoric acid is hard to recycle and fluorine impurities are hard to separate from phosphoric acid concentrated sludge acid, a sludge acid byproduct fertilizer is high in fluorine content, and the potassium element cannot be efficiently utilized, are solved.