The rapid development of Beijing-Tianjin-Hebei Urban Agglomeration (BTHUA) has significantly raised the quality of life in the region. However, but it also has a negative impact on the ecological environment. Using the panel data of BTHUA from 2000 to 2015 as the research sample, the stress-state-response (PSR) index system of collaborative consultations on ecological security was constructed. The TOPSIS and gray correlation methods were used to measure the Comprehensive Index of Ecological Security (CIES), and then the key factors were extracted by factor analysis. The influence of these factors on ecological security was calculated by Multiple Linear Regression. The results reveal that the eco-security index (ESI) of BTHUA has reached the early warning state, showing the "North High South, West High East low" spatial pattern. Therefore, there is an urgent need to establish an ecological security mechanism. The ESI of BTHUA fluctuated slightly, which was attributed to the planning and policy implementation of urban agglomeration. There were significant differences in the evolution trends of the ESI of the 13 cities, with Chengde and Langfang showing a downward trend. The factors urbanization, social development, and technological progress have significant positive correlation with ecological security in BTHUA, while the level of development, economic development, and ecological pathology have negative correlation. Therefore, it is necessary to delineate and strictly adhere to the red line of ecological protection of urban agglomerations and control the magnitude and speed of physical space development in order to curb ecological deterioration. Improving the coordinated development planning system of BTHUA and its policies is important to ensure steady improvement of ecological security in urban agglomerations. At the same time, urban agglomerations should control the pace of economic development, upgrade the level of social development, and establish an integrated social service guarantee system. Furthermore, urban agglomeration should enhance the level of ecological technology research and development, and increase the protection and restoration of ecological spaces to reduce the risks to ecological security.