Until now, studies on trade-offs and synergies of ecosystem services were mostly on a local scale. Key vulnerable ecological areas have been the main target areas for improving the ecological environment in China. Based on the quantitative assessment of soil conservation, vegetation net primary productivity (NPP), and water production services in key vulnerable ecological areas of China from 1990 to 2015, we studied the trade-off and synergy of ecosystem services using the correlation coefficient method and vegetation continuous fields (VCF) data. The results showed that:(1) during the 26 years, the soil conservation services, NPP and water production services in key vulnerable ecological areas showed a distribution pattern of more south and less north, and the interannual variations of the three services were smaller, but they all had an upward trend; (2) the three ecosystem services in the investigated key vulnerable ecological areas were synergistic as a whole and partially balanced, and the synergistic relationship is weakening; (3) the ecological service area's ecosystem service synergy is greater than the non-ecological in the recovery area, the dynamic change trend of the weakening of the trade-off relationship is higher than that of the non-ecological recovery area. Quantitative assessment of the spatial and temporal characteristics of trade-offs and synergies of ecosystem services would be useful for studying the temporal nonlinearity and spatial heterogeneity of the relationships among ecosystem services, and it would be of great significance for the sustainable development of ecosystems in key vulnerable ecological areas.