Although there have been tremendous achievements ever since the first work on an organic electroluminescent (EL) device that emitted polarized light, the development of flexible polarized emission organic light-emitting devices (OLEDs) is not without hurdles, and the challenge towards real-world applications still requires tremendous effort. In this paper, we proposed highly linearly polarized light-emission from flexible green OLEDs capitalized on integrated ultrathin metal-dielectric nanograting. The acquired polarized device with meticulously optimized geometric parameters yields an angle-invariant average extinction ratio beyond 20.0 dB within a viewing angle range of ± 60°. The detailed analysis illustrates that surface plasmons and cavity modes are simultaneously contributed to the TM-polarized light selection. We hope that the presented approach will open new opportunities for designing flexible polarized light sources.