[Objective] An urban ecological security system with relatively complete regional environmental characteristics and social development level for Beijing City was constructed in order to provide a scientific reference for effectively controlling the ecological security bottom line for urban expansion and development, and thereby protect urban biodiversity.[Methods] The ecological sources for Beijing City were extracted based on water conservation, biodiversity maintenance, wind and sand fixation, soil and water conservation, and various nature reserves in the city. A multi-factor index that considered the whole domain by using a minimum cumulative resistance (MCR) difference model (namely the ecological source expansion resistance and surface resistance difference) was used to divide the national urban sprawl spatial pattern of ecological land, such as high level ecological area, medium level ecological area, low level ecological area, ecological town critical area, low level urban construction area, medium level urban construction area, and high level urban construction area. The ecological corridor and ecological node area were identified in order to construct a land security pattern for Beijing City.[Results] The total area of ecological sources in Beijing City was 3 568.95 km², accounting for 21.7% of the total land area of the entire region, which was concentrated in the northwest part of Beijing City and surrounded the central and western urban areas. There were 11 important ecological corridors and 153 ecological nodes, of which Shijingshan District had the largest ecological network density and Dongcheng District had the smallest ecological network density. The construction area in the center of Beijing City was spreading in the pattern of a "spreading big cake", and the degree of rupture of ecological corridors in the city was high.[Conclusion] The ecological pattern of Beijing City is obviously fragmented. In the future, the spatial layout of ecological nodes should be optimized to obtain ecological benefits by protecting ecological sources, planning ecological corridors, and controlling the construction of critical areas of ecological towns.