Abstract: Lithium niobate on insulator (LNOI) combines the excellent linear and nonlinear optical properties of lithium niobate (LiNbO₃) crystals with advantages of facile photonic device processing and integration, and is considered as one of the potential platforms for integrated optics. In this study, we fabricated an L-shaped LNOI metasurface structure by an inductively coupled plasma reactive ion etching system (ICP-RIE) system, and proposed an optimization strategy to enhance the traditional process. The method involves correcting the exposure pattern to precisely control the L shape, reducing the coating rate to improve mask density and uniformity, and adjusting etching gas composition by introducing hydrogen to eliminate the by-products of the sample. The experimental results show that this optimized process significantly improves the surface flatness of the L structure, increases the sidewall steepness, and ensures the dimensional conformity with the theoretical design. The second harmonic generation (SHG) intensity is approximately five times higher than that of LNOI. This study promotes the development of the preparation and integration technology of lithium niobate crystal optical components.