Under the background of urban expansion and global climate change, the delta social-ecological system is suffering from various risks. Nowadays, it has become a global risk hot spot area and the epitome of global sustainable development. This study assessed the regionally ecological risk of the study area from the perspective of adaptability, which helps to understand the interaction between complex system and risk impact. And it provides a spatial quantitative reference for the adaptive planning strategy of Yangtze River Delta urban agglomeration. It is of great significance to the ecological adaptability planning of the social ecosystem of the Yangtze River Delta urban agglomeration. The research object of this study is the social ecological system of Yangtze River Delta urban agglomeration. In this study, the adaptive cycle and ecological risk assessment theory were coupled to construct the "potential-connectedness-resilience" adaptive ecological risk assessment framework. From the overall and dynamic point of view, the paper evaluated the current and future adaptive ecological risk, and the adaptive cycle phase of each city in the Yangtze River Delta urban agglomeration was further identified and analyzed according to the risk eigenvalues. The results show that the adaptively ecological risk from coastal area to urban agglomeration and ecological region presents a trend from higher to the highest and then to low. Moreover, due to the expansion and development of cities, the suburbs of big cities are now at higher risk. By 2030, the overall ecological risk will increase. The development and construction of small and medium-sized cities, urban expansion and occupation of ecological space and climate change will lead to the spread of the high-risk areas to small-medium cities and ecological regions. In terms of the adaptive cycle stage of ecological risk, 14 cities such as Hangzhou and Ningbo are in reorganization phase with low ecological risk; 8 cities such as Changzhou and Nantong are in the exploitation phase of increased risk; Shanghai, Nanjing, Wuxi and Suzhou are in the conservation phase. At this stage, the urban development and construction are basically completed, and the regional ecological risk begins to reduce. In the study, the distribution of high-risk areas and the adaptive risk trend of each city were obtained by evaluating the adaptive ecological risk of Yangtze River Delta urban agglomeration. It provides the scientific guidance for the formulation of adaptive planning strategies under the dynamic changes of Yangtze River Delta urban agglomeration, so as to realize the sustainable development of the region. And it promotes the green transformation of Yangtze River Delta urban agglomeration, and forms ecological urban agglomeration of sustainable development.