Abstract:[Objective] The functional composition of the soil and water conservation ecological services in Mudanjiang City, Heilongjiang Province, China, was constructed from the perspective of ecological priority. The spatiotemporal differentiation characteristics, tradeoffs and synergies of regional soil conservation, carbon sink of soil and water conservation, and water purification capacity were explored, and the intensity of regional soil and water conservation ecological services was calculated, providing scientific basis for maintaining regional ecological stability, ensuring the sustainable development of agriculture, and improving hydrological connectivity and water quality. [Methods] The main watershed and sub-watershed of Mudanjiang City were divided using the SWAT model, and the soil and water conservation ecological service functions (soil conservation, carbon sink of soil and water conservation, and water quality purification) were quantitatively evaluated and analyzed in terms of space and time in each watershed for 2002, 2012, and 2022 using the InVEST model. The soil conservation function was analyzed using bivariate spatial autocorrelation analysis at the grid scale based on the Geoda software. We studied the tradeoff and synergistic relationships between the different service functions and their temporal changes and calculated the ecological service intensity of soil and water conservation in Mudanjiang City by combining numerical and weighting methods. The contributions of rainfall and the digital elevation model to each service function were explained using geographic detectors. [Results] The soil conservation and soil and water conservation carbon sink functions in Mudanjiang City exhibit a synergistic relationship, whereas the water quality purification function exhibits tradeoff relationships with both the soil and water conservation carbon sink and soil conservation functions. The average ecological service intensities of soil and water conservation in 2002, 2012, and 2022 were 0.327 5, 0.325 6, and 0.332 7, respectively, showing a slight decrease followed by an increase. [Conclusion] The soil and water conservation ecological service functions in Mudanjiang City improved compared to the case in the initial study period, with the average value in Suifenhe River basin being better than those in other regions and Mudanjiang River basin contributing the most to the total. The spatiotemporal heterogeneity characteristics of the service functions are affected by precipitation, topography, land use change, and vegetation coverage.