Abstract: The coastline, a critical eco-geomorphological boundary at the land-sea interface, is of significant importance for coastal zone resource management, ecological conservation, and spatial planning. Accurately extracting its information is therefore essential. This study, based on multi-resolution remote sensing imagery, systematically analyzes the scale effect of information extraction for China's mainland coastline. For the entire mainland coastal zone, remote sensing images at 30m, 16m, and 10m resolutions were integrated; for typical regions, satellite images at 4m, 2m, and 1m resolutions were utilized. Coastlines were extracted using an expert classification (visual interpretation) method, and the lengths and classified lengths derived from different resolutions were statistically analyzed at four hierarchical levels: the overall mainland, marine areas, provincial districts, and typical regions.The results indicate that:(1) The total length of China's mainland coastline increases as image resolution improves, growing from 17,567.55 km (30m) to 18,206.73 km (16m), and 19,152.17 km (10m). The coastline is dominated by natural and aquaculture shorelines; notably, the proportion of aquaculture shorelines increases with higher resolution, while the proportion of natural shorelines correspondingly decreases.(2) At the marine area level, coastline lengths in all regions significantly increase with improved resolution, though the magnitude of increase varies markedly. The North Yellow Sea exhibits the largest relative increase (16.6%), whereas the South China Sea exhibits the smallest (5.3%).(3) Significant differences are observed at the provincial level. Liaoning, owing to its intricate bedrock coasts, experiences the largest resolution-dependent increase in length. Conversely, Shanghai and Tianjin, characterized by highly artificialized shorelines, show the minimal increases.(4) At the typical region level, coastline length increases significantly as resolution improves from 30m to 1m. Artificialized or intricate coastal segments show a more pronounced response. Notably, the rate of increase in length tends to slow down once the resolution is finer than 4m.(5) Regarding coastline length measurement, 4m resolution effectively balances accuracy and efficiency, making it a suitable scale for extracting macro-scale morphological features. However, for the precise interpretation of coastline types, incorporating higher-resolution imagery (e.g., 2m, 1m) is advisable to achieve reliable identification and classification of fine-scale, fragmented segments. This study reveals the systematic response characteristics of coastline length and type-structure information extraction to image resolution, providing high-precision foundational data and methodological support for China's coastal zone protection, shoreline resource management, and further research into scale effect mechanisms.

Key words: coastline, multi-scale remote sensing, scale effect, coastal zone management, mainland China