The composition of multilayered chromium-nitride-carbon (Cr-N-C) film has great influence on the performance of coated 316L stainless steel (SS316L) as bipolar plates for proton exchange membrane fuel cells (PEMFCs). In this study, five films with different composition are deposited by closed field unbalanced magnetron sputter ion plating (CFUBMSIP) and the influence of nitrogen content adjusted by a closed-loop optical emission monitor (OEM) is evaluated. The phase structure and chemical composition of the films are characterized by X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Interfacial contact resistance (ICR) between coated samples and gas diffusion layer (GDL) is measured. Potentiodynamic and potentiostatic tests are conducted to evaluate the corrosion resistance of coated samples. Experimental results show that Cr-N-C film with OEM setting of 60% presents the best performance, i.e. the ICR reduces to 2.11 mΩ cm2 under a compaction pressure of 1.4 MPa, and the corrosion current density reaches 0.308 μA cm−2 in the PEMFCs cathodic environment (0.5 M H2SO4 + 5 ppm HF solution at 70 °C, 0.6 V vs. SCE). Therefore, this study indicates that Cr-N-C film with OEM setting of 60% achieves optimal film composition and may be practically applied for commercialization of PEMFCs technology.