珊瑚沙岛是热带海洋中常见的地貌类型，具有重要的生态功能与科学研究价值，近年来全球气候变化加剧及人类活动增加，对珊瑚沙岛的稳定性和生态环境构成了严峻挑战。本文以南海西沙群岛的典型珊瑚沙岛——北岛为研究对象，基于2002至2023年多期高分辨率遥感影像数据，结合数字海岸线分析工具，分析了北岛的岸线变迁规律及海滩岩的退化过程。研究进一步探讨了岛屿演变的驱动因素，并提出相应的防护对策。研究结果表明：（1）北岛岸线长度和面积呈现先增后减趋势，在2019年达到最大值；2015-2019年间，填海造陆导致岸线显著扩张，而2019-2023年间，岛屿遭受侵蚀最为严重；北岛沙嘴区域的变化最为显著，在季风影响下，呈现出东北季风导致侵蚀、西南季风引发淤积的特征，沙嘴以季节性变化为主，年际变化较小；北岛海滩岩则在人类活动的干扰下急剧减少。（2）珊瑚沙岛演变的本质是水动力与沉积物的相互作用，海岸水动力变化、珊瑚礁退化、全球气候变化以及人类活动干扰等因素共同驱动了珊瑚岛的演变。（3)本文提出了分层生态保护对策，从潮上带到潮下带逐层防护，采用植被固沙、移动固沙障、菱形固沙袋、海滩岩修复等措施，兼顾生态保护和岛屿防护需求，为南海珊瑚沙岛礁的保护与管理提供了切实可行的参考。

Coral sand islands are common geomorphic features in tropical oceans, holding significant ecological functions and scientific value. However, intensified global climate change and increased human activities in recent years have posed severe challenges to their stability and ecological environments. This study focuses on North Island, a representative coral sand island in the Xisha Islands of the South China Sea. Using high-resolution remote sensing imagery from 2002 to 2023 and digital shoreline analysis system（DSAS), we examined shoreline dynamics and beachrock degradation on North Island. The study further explored the driving factors of island evolution and proposed targeted protection strategies. The results indicate that: (1) The length and area of North Island's shoreline initially increased and then declined, reaching their maximum in 2019. From 2015 to 2019, land reclamation significantly expanded the shoreline, while from 2019 to 2023, severe erosion occurred. Changes in the island's sandy spits were the most pronounced, displaying erosion under the influence of the northeast monsoon and accretion during the southwest monsoon, with seasonal variability exceeding interannual changes. Beachrock on North Island has rapidly diminished due to human interference. (2) The evolution of coral sand islands is fundamentally driven by interactions between hydrodynamics and sediment. Coastal hydrodynamic changes, coral reef degradation, global climate change, and human activities collectively drive the transformation of coral islands. (3) This study proposes a stratified ecological protection strategy, involving multilayered measures from the supratidal to subtidal zones. Techniques such as vegetation-based sand stabilization, mobile sand barriers, diamond-shaped sandbags, and beachrock restoration balance ecological conservation with island protection needs, offering practical insights for the protection and management of coral sand islands in the South China Sea.