The invention discloses a method for preparing sulfonated polymer films, which comprises the following steps: preparing a casting solution and film-forming on the basis of phase-inversion. The sulfonation reaction is carried out between one or two of polyether-ether-ketone (PEEK), phenolphthalein polyaryl ether sulfone (PES-C) or polystyrene (PS) and concentrated sulfuric acid, fuming sulfuric acid or chlorosulfonic acid to obtain a sulfonated polymer solution in the preparation of the casting solution; and then, the film is directly formed on the basis of the phase-inversion method. The sulfonated polymer film prepared by the invention has higher pure water flux and protein retention rate, furthermore, the method has the advantages of good anti-pollution performance, higher mechanical strength and simple preparation process.