我国南海海疆线的研究主要基于九段、十一段线等断续线的法律和历史属性，对其自然属性研究基本处于空白。团队前期工作新报道了1951年出版的完整南海U形海疆线（简称南海U形线）历史地图，佐证了南海U形线的海疆国界线重要地位。本项目将首次开展该南海U形线的自然环境研究，分析其水深特征并分区研究。（1）南海U形线定位。根据新报道的南海U形线地图提取经纬度定位完整U形线；（2）南海U形线水深地形。用卫星、航测数据和GIS技术，研究南海U形线三维水深特征；（3）南海U形线分区。依据地形特征，提出南海U形线分区方法；（4）南海U形线海洋环境。分析南海U形线海洋要素季节和年际变化特征，揭示其环境变化的影响因素。该课题引领整体南海U形线的研究，弥补对南海疆界线自然属性认识的不足，弥补“断续线”的不足，是“一带一路”、维护南海主权的国家战略需求，为南海问题下一步走向提供策略选择，有重大科学和指导意义。

The previous studies on the Chinese boundary of the South China Sea have been mainly based on the legal and historical attributes of the intermittent lines such as the Ninth Section and the Eleventh Section Line. The research on its natural properties is basically blank. Our previous work reported a complete historical map of the Chinese U Boundary of the South China Sea (referred to as the U boundary) published in 1951, which corroborated that the U boundary is Chinese boundary in the South China Sea. This project will carry out a study on the natural environment of the U boundary in the South China Sea, analyze its water depth characteristics and conduct a zoning study for the first time. (1) U boundary positioning. According to the newly reported map of the U boundary in the South China Sea, the latitude and longitude of the whole U boundary will be extracted; (2) terrain of U boundary in the South China Sea. Using satellites data, aerial survey data and GIS technology, the three-dimensional characteristics of water depth among U boundary in the South China Sea will be studied; (3) Partition of U boundary in the South China Sea. Based on the topographical features, the division method of U boundary in the South China Sea will be proposed; (4) Marine environment of U boundary in the South China Sea. The characteristics of the seasonal and inter-annual changes of the marine elements of the U boundary in the South China Sea will be analyzed to reveal the influencing factors of their environmental changes. This topic leads the study of the overall U boundary in the South China Sea, making up for the lack of understanding of the natural attributes of the boundary line in the South China Sea and the inadequacies of the “intermittent line”. It is a national strategic demand for the “The Belt and Road” and safeguarding the Chinese sovereignty within the boundary in the South China Sea. It is of great scientific and guiding significance to provide strategic choices for the next step of the South China Sea issue.