Providing water resources is one of the most important ecosystem services functions and plays an important role in the sustainable development of regional economy and ecosystem. In recent years, the increased demand for water resources, water pollution and serious waste of water resources due to the human activities result in the water shortage problems in some areas. Under this background, we used Ningbo region as an example to study the impacts of climate and land use/land cover (LULC) changes on water yield service. Firstly, the water yield module of the InVEST model was used to estimate the water yield in the study area. Secondly, six scenarios were designed to analyze the impacts of climate and LULC changes on regional water yield. Finally, the contribution of two factors on water yield ecosystem services was quantified, including climate and LULC changes, and the formation mechanism was discussed. The results show that:①From 2000 to 2015, the precipitation increased by 6.44% and the potential evapotranspiration decreased by 8.35% in Ningbo region. Urbanization caused an increase of 120% in construction land area, and 22.37% in the cultivated land area. Under the combined effects of climate and LULC changes, the average water yield increased by 10.91%. ②The impact of climate change on water yield service is more significant than that of LULC change. Specifically, the contribution of climate change to the water yield is as high as 97.56%, while the contribution of LULC change is only 2.44% in Ningbo region from 2000 to 2015. ③The water yield of urban ecosystem is the highest of any other types of ecosystem. The water yield of farmland ecosystem is higher than that of forest and grassland ecosystem. Therefore, the urbanization would increase the amount of water yield, however the returning farmland to forest or grassland would result in a decrease in water yield.