In the proton exchange membrane fuel cell (PEMFC) with widely applicated future, the bipolar plate plays an important role in supporting the cell stack, collecting current, separating the oxidants from fuels and channeling the oxidants and fuels. The ideal bipolar plate should be of good electric conductivity, high corrosion resistance, high mechanical strength, low gas permeability, low cost and easy processing. Although the stainless steels can be used as bipolar plate materials, their corrosion resistance in fuel cell environment is not satisfied, and the cations induced by metal corrosion would poison the proton exchange membrane. A series of Cr_1-xN_x (x=0.28-0.50) films were deposited on the surface of stainless steel by arc ion plating (AIP), the composition and phases of Cr_1-xN_x films and the electric conductivity and corrosion resistance of the modified bipolar plates were tested. The results show that as the value of x varying from 0.28 to 0.50, the phases in the films change from Cr+Cr₂N to Cr₂N, then to Cr₂N+CrN and finally to CrN. The bipolar plates coated with the Cr_1-xN_x film with single phase structure show good electric conductivity and high corrosion resistance. Comparing with the original stainless steel, the electric conductivity and corrosion resistance of bipolar plates are enhanced by more two orders of magnitude and almost three orders of magnitude, respectively.