With the rapid development of photonic integration and optical communication technology, low-loss waveguides have become the key components for efficient photonic transmission, and their performance directly affects the performance of the entire integrated chip. Therefore, the preparation technology of low-loss thin film lithium niobate (TFLN) waveguides is currently a hot and difficult research topic. In this study, in-depth research on the preparation process of wafer-level low-loss thin-film lithium niobate waveguides was conducted. On a 4-inch thin-film lithium niobate wafer, waveguides with a transmission loss of less than 0.15 dB/cm based on the deep-UV lithography and inductive coupled plasma etching were successfully prepared, while the etching depth error was controlled within 10%, greatly improving the accuracy of the waveguide structure. Additionally, this study also proposed a characterization method based on micro-ring resonators for wafer-level waveguide loss measurement, which can more accurately evaluate waveguide performance. Through testing, it is found that the qualified rate of the prepared waveguides exceeds 85%, demonstrating good reproducibility and reliability. The wafer-level thin film lithium niobate processing technology developed in this article is of great significance for promoting the large-scale preparation and application of lithium niobate waveguides.