Maintaining ecosystem health in urban agglomerations is a critical priority in the construction of an ecological civilization, and scientific measurement of ecosystem health is the basis for achieving effective protection. Taking the Beijing-Tianjin-Hebei region as an example, this study systematically analyzed the spatial and temporal changes of ecosystem health in the region between 2000 and 2020 based on three scales: county, village, and raster, and explored the differences in the impacts of the natural environment and socioeconomic factors on ecosystem health. In addition, this study simulated the trend of ecosystem health changes in the Beijing-Tianjin-Hebei region under three different development scenarios of natural development, ecological protection and economic development in 2035, and revealed the spatial scale effects of ecosystem health. The results of the study are as follows: (1) At the county, township and grid scales, the overall ecosystem health showed a decreasing trend, with the most significant decrease at the grid scale, followed by the township scale, and a relatively small decrease at the county scale; the spatial distribution pattern of ecosystem health showed a decreasing characteristic from north to south, and there was obvious spatial heterogeneity. (2) In terms of influencing factors, the Beijing-Tianjin-Hebei region was significantly influenced by natural conditions such as average annual precipitation and topographic relief in the early period. With the rapid socio-economic development, economic factors such as population density and land-use intensity began to gradually dominate in the later stage; there are also differences in the explanatory power of the influencing factors at different scales. (3) The outcomes of the multi-scenario forecasts suggest that by the year 2035, the Beijing-Tianjin-Hebei region is projected to exhibit the most robust average ecosystem health within the ecological protection scenario. The natural development scenario is anticipated to rank second in terms of ecosystem health, whereas the economic development scenario is expected to present the most fragile state of ecosystem health among the three. (4) Ecosystem health has a clear spatial scale effect. Specifically, larger scales may lead to more homogenized ecosystem health assessment results, thus masking key regional ecological health issues; conversely, smaller scales may provide a finer picture of ecosystem health, but may also over-amplify local details. Thus, it is important to choose the appropriate spatial scale according to the actual situation. This study provides insights into the interaction between ecosystem health and socioeconomic development of urban agglomerations in the context of new urbanization, which is an important reference for promoting high-quality development and ecological environmental protection in urban agglomerations.