In order to understand the spatialtemporal change characteristics of ecological spaces in the plain areas of Beijing, and to identify places that are key for improvement during the largescale afforestation project, we studied the relevant variations of ecological spaces between 1992 and 2013 using 3S (RS, GIS and GPS) technology and landscape analysis methods. The results showed that the percentage of ecological space in Beijing’s plain areas dropped from 53.2% to 40.97% during this period. Per capita share of the ecological spaces also deceased from 360.61 m² to 132.15 m². From the city’s center to the suburb area, ecological spaces tended to be more abundant and aggregated, but this distribution gap seemed to be narrowed with time. Ecological spaces in the south and southeast of Beijing’s plain areas decreased dramatically during the past 22 years, as well as per capita share in the areas between the 5th and the 6th Ring Road. Ecological spaces along the 3rd Ring Road were highly fragmented. The main composition of ecological spaces within a 5 km radius circular area of separated towns or communities in Beijing’s plain areas gradually transformed from grasses/croplands into woods/shrubs during the 22 years. These changes might be driven by population explosion, urban sprawl, and the transformation of traditional croplands to plastic greenhouses or other land use types, while planting of urban forests in Beijing’s plain areas have continually made positive contributions to ecological spaces’ maintenance and restoration. The recent large-scale afforestation project in this area would provide a new golden opportunity for adjusting its ecological spaces. Besides, protection of water and croplands should also be emphasized along with increasing the forest cover.