A low-loss and compact TM-pass polarizer is demonstrated based on improved hybrid plasmonic grating (HPG) on a Z-cut lithium-niobate-on-insulator (LNOI) platform. In this work, we introduced the silica partition structures surrounding an LN (LiNbO₃) ridge waveguide to support two parallel metal gratings, achieving the optimal coupling coefficient for HPG. Compared with the traditional HPG structure, the transverse electric (TE) mode suffers a higher confinement and the transverse magnetic (TM) mode transmission loss exhibits a significant reduction in the improved HPG structure. The simulation shows that the polarizer achieves a broad bandwidth of 150 nm (1500 to 1650 nm) with an extinction ratio (ER) over 20 dB and an insertion loss varying from 0.18 to 0.3 dB, including a maximum ER of 36 dB at the wavelength 1550 nm. In addition, the length of the demonstrated polarizer is only 10 μm, making it compact for integration. The proposed polarizer shows a good application prospect for integrated photonics in LNOI.