The work aims to improve the corrosion resistance of proton exchange membrane fuel cell (PEMFC) bipolar plates. Conductive polyaniline (PANI) films were electrochemically synthetized on the surface of 316L stainless steel (SS) by cyclic voltammetry to prepare PANI/316L SS composite bipolar plates. The PANI functional group structure was determined by FTIR, the surface morphologies were observed by SEM, and the composition and bonding state of the PANI film were investigated by XPS. The corrosion environment of PEMFC was simulated by 0.2 mol/L H2SO4, the corrosion resistance of PANI/316L SS was studied by polarization curve, and the corrosion behavior of PANI/316L SS during long-term immersion was investigated by open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). PANI film had an intermediate oxidation structure and exhibited fiber packing morphology. XPS results showed that PANI film contained C, N, S and O elements, and the “counter anion” SO42- entered PANI molecular chains by “doping” during the polymerization process. The corrosion potential of 316L SS coated with PANI film was increased by 0.17 V and OCP was between 0.19 V and 0.32 V, indicating that the corrosion tendency of PANI/316L SS was decreased during long-term immersion. The increase of OCP at the initial stage of immersion corresponded to the formation of passivation film at the film/base interface, the decline/rise of OCP at the middle stage of immersion was related to the dissolution/repair of passivation film, and the continuous decline of OCP at the later stage of immersion was due to the dissolution of passivation film. Nyquist plots of EIS were composed of the capacitive reactance arc at high frequency end and diffusion tail at low frequency end. PANI film is oxidized, which leads to the “de-doping” of the “counter anion” SO42- from PANI, making the film resistance increase and the arc radius of the capacitive reactance increase with the prolonged immersion time. The PANI/316L SS has good corrosion resistance after being soaked in 0.2 mol/L H2SO4 solution for 82 days.