Abstract: In the process of transition from traditional agriculture to modern agriculture, the role of agriculture has been changing from single to multiple functions. Comprehensive evaluation of the degree of synergy of agro-ecosystems can guide sustainable regional development. The dry farming area in Northeast China is not only an important grain production base, but also a severe soil erosion area in China. Due to excessive long-term fertilizer application, unreasonable farming systems and management measures, agro-ecological environments in the dry farming areas have faced enormous pressure. In this research, the grain production and soil data for 85 counties in dry farming areas of Northeast China were used as basic materials, which included socio-economic data from agricultural statistics yearbooks of three northeastern provinces from 2005 to 2015 and soil physic-chemical parameters obtained from soil samples collected in the study area in May 2017. The spatial variations in synergy and trade-offs among agro-production functions, agro-living functions and agro-ecological functions of agro-ecosystem were analyzed based on the synergetic model and root mean square error (RMSE) at different time periods. The aim of this research was to reveal the temporal and spatial evolution characteristics of the three agro-ecosystem functions stated above. The results showed that the degree of the synergy of agro-ecosystem was low for the dry farming areas in Northeast China, dropping by 0.12 for the period 2005-2015. The degrees of synergy of agro-production function and agro-ecological function were dropped by 0.03 and 0.45, respectively. However, the synergy degree of agro-living function increased slightly. Except for drying farming areas in Liaoning Province, the synergy degree of agro-ecosystem decreased significantly in Jilin Province and Heilongjiang Province, indicating that the synergy among three functions of agro-ecosystem was in disorder. There were spatial and temporal trade-off relationships among various functions of agro-ecosystem. For the period 2005-2010, the trade-offs between agro-production function and agro-ecological function, and between agro-living function and agro-ecological function benefited from the ecological function. However, the trade-offs benefited from the production functions and living functions for the period 2010-2015. The main reasons were the fluctuations in the trade-off relationships among three functions of agriculture and changes in the related benefit directions. It was suggested that the synergy degree of agro-ecosystem and the relationships among agro-production function, agro-living function and agro-ecological function were quantitatively describable using the synergetic model and root mean square error. It was an effective way of identifying the structural factors that caused changes in agro-ecosystems by the two methods. The results provided critical references for sustainable development of agro-ecosystem in the dry farming areas of Northeast China.