Abstract: Coordinating the trade-offs between ecosystem services is the key for effective ecosystem management and sustainable development. The present study used the ecosystem service evaluation models and monetary evaluation method to evaluate the spatial distribution of five key ecosystem services of Tianmu Lake catchment in 2019, i.e., water conservation, water purification, soil retention, carbon sequestration and product supply services. Then, the synergism and tradeoffs among different ecosystem services were assessed. In addition, a multi objective genetic algorithm (NSGA-Ⅱ) was used for the spatial optimization of water purification service and supply service. The results showed that: (1) water conservation, water purification, soil conservation and carbon sequestration services showed high values in the southern and low values in the northern part of the Tianmu Lake catchment, and exhibited obvious positive correlation with the vegetation coverage. Whereas high values of product supply service were mainly found in the middle part of the catchment and along the river, where tea gardens and cultivated land were densely distributed. (2) synergistic relationships were found for water conservation, water purification, soil conservation, and carbon sequestration services, whereas product supply service showed trade-off relationship with all other services, among which the trade-off relationship with water purification is the strongest and showed as the most prominent contradiction in the catchment. (3) The NSGA-Ⅱ algorithm provided four schemes for the multi-objective optimization of ecosystem services in the study area. All proposed optimization schemes could resolve the conflicting relationship between water quality purification and economic output for a certain extent. The present study could provide new insights and methods for the sustainable management and space layout optimization in Tianmu Lake catchment and other headwater catchments.