Based on the transverse electric (TE)/transverse magnetic (TM) polarization diversity in plasmonic Bragg gratings, a compact TM-pass/TE-stop polarizer is theoretically proposed on thin-film lithium niobate on insulator (LNOI) platforms. By introducing a large misalignment between metal gratings on both sides of the LNOI waveguide, we demonstrate a polarizer with a high extinction ratio of 20 dB, a low insertion loss of 2.5 dB, a wide waveband from 1.48 to 1.62 µm, and a compact size of only 23 µm on simulation. © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement