Abstract: Based on Landsat imagery from 1985–2025, an integrated MNDWI-Otsu-Canny algorithm was applied to extract a 40-year shoreline time series of the Sanggou Bay, Weihai, Shandong. A multi-source data fusion framework was established combining satellite remote sensing, UAV photogrammetry, and RTK positioning, and the EOT20 tidal model was employed to normalize multi-temporal shorelines to a mean sea level (MSL) datum. Sandy shoreline segments were quantitatively analyzed using the Digital Shoreline Analysis System (DSAS), and results were interpreted together with ERA5 wind-wave reanalysis data, tidal current observations, and the history of coastal development to elucidate the shoreline evolution patterns and driving mechanisms. Results indicate: (1) the shoreline has been obviously artificialized. Over the 40-year period, the total shoreline length increased from 49.41 km to 55.05 km, of which the artificial proportion rose from 24% to 55% and has become the dominant type, while sandy and rocky shorelines declined continuously. (2) Sandy shorelines exhibit an overall erosional trend, and the mean Net Shoreline Movement of −17.33 m, End Point Rate of −0.43 m/a, and Linear Regression Rate of −0.17 m/a were noticed, displaying a distinct spatial pattern of "light erosion in the north, intensive erosion in the south, and accretion in both flanks". (3) Shoreline evolution is driven by the coupled effects of natural dynamics and anthropogenic activities. Wave action serves as the primary controlling factor, exerting persistent erosion on sandy shorelines; tidal asymmetry and geomorphological configuration jointly regulate the sediment transport patterns. Combined with human activities, these multiple factors interact to drive shoreline evolution. This study innovatively integrates UAV-RTK high-precision topographic surveying with Landsat time-series remote sensing, applying a tidal position correction method based on measured intertidal slope gradients, which effectively reduced systematic errors in shoreline extraction caused by tidal range variations and provided a quantitative basis for uncertainty assessment in long-term shoreline evolution analysis. This research revealed the evolution mechanisms of shorelines in a semi-enclosed bay and offered scientific guidance for shoreline management and sustainable coastal zone governance in Sanggou Bay.