Ecological security network is an important framework for maintaining the structural integrity and functional diversity of the urban ecosystem. The interconnected ecological elements are of great significance for balancing construction and sustainable development of the urban ecosystem. Taking Yichang City, where the Three Gorges Dam is located, as the object, the ecological security network was constructed based on the paradigm of "ecological source, ecological resistance, ecological corridors, ecological pinch points, and ecological barriers". We analyzed the spatio-temporal dynamics of different ecological security network elements in 2000, 2010, and 2020 and explored the influencing mechanism. The results showed that:(1) the ecological source was identified based on the MSPA (Morphological spatial pattern analysis), habitat quality aggregation analysis, landscape connectivity analysis, and natural reserve area analysis. In 2000, 2010, and 2020, the area of the ecological source was 43.41×10⁴, 49.03×10⁴, and 47.76×10⁴ hm², respectively. They were concentrated in the Three Gorges Dam water and soil conservation zone. The number, length, and area of the ecological corridor decreased gradually from 2000 to 2020. The number and length of the ecological corridor were mainly concentrated in the plain shallow mound ecological construction zone, while the area was mainly concentrated in the Three Gorges Dam water and soil conservation zone. The number and area of the ecological pinch point first increased and then decreased from 2000 to 2020. They were concentrated in the Three Gorges Dam water and soil conservation zone. The number and area of the ecological barrier were concentrated in the Three Gorges Dam water and soil conservation zone and the plain shallow mound ecological construction zone. (2) The value of the ecological resistance was 38.90, 42.19, and 40.66, respectively. They increased gradually from west to east. The resistance value of the plain shallow mound ecological construction zone was significantly higher than that in other zones; (3) The influencing mechanism of the ecological source showed that the precipitation had the strongest explanatory effect, while the soil type had the weakest effect. The interaction between different influencing factors showed that the precipitation and other factors had more intense interaction. The systematic discussion on the spatio-temporal heterogeneity of the ecological security network elements and its impact mechanism in Yichang explained the development trend and the potential challenge of the current situation of ecological security network. It could provide scientific support for the construction and management of related projects of ecological security network, such as the Three Gorges Barrier Construction Project.