High-intensity land use and fragmented habitats are becoming more prevalent with urbanization, thereby accelerating the demand for maintaining and improving the ecological connectivity of habitat patches in high-density built-up areas. Previous studies have shown that small dispersed patches are crucial for enhancing connectivity across an entire landscape. However, as an important component of urban green space, residential green space in high-density built-up areas is often overlooked in ecological connectivity analysis. Taking Futian district, Shenzhen, as a case study, we explored the ecological connectivity in high-density built-up areas considering not only habitat patches but also green areas in residential quarters. We identified ecological patches and green areas in the residential areas of the study area. This was followed by a functional connectivity analysis under different scenarios. Several protection suggestions for improving ecological connectivity have been proposed based on functional connectivity analyses under different scenarios. The results show: 1) The area of residential green space in Futian district is 3.86 km2, covering 26.9% of the total green space in the study area, with the western part being sparser than other regions. The total area of the ecological patches was 14.34 km2, and the importance of the patches was not consistent with their size. The ecological connectivity of Lianhuashan Park in the central region, Lichi Park in the eastern region, and Huanggang Park in the southern region is greatly affected by the contiguous or continuously distributed strips of residential green space around them. 2) Residential green spaces affect eco-connectivity primarily by lowering corridor resistance, creating connectors for regions that require protection, and supporting biological flow. In particular, it had the largest effect on middle-resistance corridors (the unit cost distance was reduced by 29.2%) and alleviated the situation of pinch points formed in narrow low-resistance channels in high-density built-up areas. 3) The ecological pinch points that recurred in the ecological network under different scenarios of connecting residential green spaces and different resistance thresholds were identified as the most valuable primary pinch points for protection. It is recommended to strengthen the intersection of Xinzhou Road and Fumin Road and prioritize the protection of residential green spaces located near the ecological patches and on the topological connection between the ecological patches, with a scale exceeding the average size of 5,920.22 m2. Through the analysis of pinch points in various scenarios, it was found that 21 pinch points, including those close to Lianhuashan Park, could be used as substitute green spaces for urban renewal projects when nearby residential green spaces are destroyed or occupied. This supports the preservation of functional connectivity in urban renewal projects. It is increasingly difficult to construct significant habitat patches in high-density built-up areas to compensate for habitat fractures. The results identified the significant location and proportion of residential green spaces as critical bio-flow carriers in Futian District. These findings could encourage more comprehensive urban conservation plans that incorporate both sizable habitat patches and residential green spaces. These findings can be used to create more effective sustainable development plans that encourage biodiversity in urban renewal planning.