Humans and nature are in an organic and dynamic equilibrium, and human beings must respect, conform to, and protect nature. However, along with continuous economic growth and urbanization, our country faces huge pressures for resources, and the environment and ecological systems are under serious threat. How to protect ecological security has become a focus for our country's sustainable development. Urban expansion is an important driving force of land use and cover change, and high-intensity human activities have greatly altered the structure of natural ecosystems, decreased ecosystem service functions, and seriously threatened regional ecological security. In recent years, a series of environmental problems have arisen, including habitat fragmentation, biodiversity reduction, and water pollution. Therefore, it is of great importance to identify ecological land and establish an ecological security pattern for regional ecological protection and sustainable development. Although there are a lot of studies about ecological security patterns in China, in most cases, the research scale is at the municipal or county level, and there are few studies at the regional scale, especially those aimed at the eastern developed areas. The study area of this research was the Sunan District, which is in the south Jiangsu Province of eastern China. It is one of the most developed and modernized regions of China with a GDP close to the level of other developed countries, and the proportion of its urban population was 75.9% in 2016.In such a fast-growing region, it is essential to establish a landscape security pattern for the coordinated development of economy and ecology. Based on the ecological background characteristics of the Sunan District, this study quantified and mapped three ecosystem services, namely biodiversity conservation, water resource security, and soil conservation, and classified ecological land into five levels (very important, important, relatively important, general, and not important) using a GIS spatial analysis method. In order to reflect differences in the impact of different land use patterns and intensities on ecological resistance under the same land use coverage type, we used nighttime light data to modify the basic ecological resistance surface which was obtained by the expert scoring method based on land-use type assignments. The minimum cumulative resistance model was used to identify ecological corridors and buffers. The ecological sources, buffers, and corridors, collectively, made up the ecological security pattern for the study area. The results showed that the area of very important ecological land was 6365.92 km² and accounted for 22.97% of the total area. When very important ecological land above 10 km² was selected as a source, the total area was 5313.31 km² and accounted for 19.17% of the total area. The ecological buffer area was 8458.79 km² and accounted for 30.52% of the total area. As for the ecological corridors, about 31.82% was farmland, 19.06% was forested areas, and 17.27% was a water body. We believe that building a comprehensive security pattern of critical ecological lands, with the advantages of spatial linkages, is an efficient spatial approach for species conservation and landscape optimization. Therefore, our results could provide a scientific reference for regional ecological and spatial layout planning for future sustainability.