This study focuses on the exploration of lithium niobate (LN) photonic crystal nanobeam cavities as a promising optical platform with a high-quality factor (Q) to mode volume (V) ratio. The LN photonic crystal nanobeam cavity was designed to exhibit a transverse-electric fundamental mode, aiming to achieve an impressive Q/V ratio of 1.6×10^7 (λ/n)^(-3), as confirmed through numerical simulations utilizing the finite element method and the finite-time time-domain method. To realize the LN photonic crystal nanobeam cavity structure, a fabrication process involving focused ion beam (FIB) milling and wet-etching was employed, resulting in a remarkable high sidewall angle of 85°. Subsequently, the characterized LN photonic crystal nanobeam cavity was coupled with a U-shaped tapered optical fiber for experimental analysis. The measured intrinsic Q factor was determined to be 6.7×10^3 and the expected Q/V is 7.9×10^3 (λ/n)^(-3). The observed discrepancy can be attributed to the downward bending effect and the insufficient buffer air layer present in the free-standing LN photonic crystal cavity.