Abstract: The transitional zone of Beijing Bay forms the mountain-plain boundary lines and rural-urban social distinctions. The balance of ecological protection and economic development dominates in the regional boundary. Therefore, there is a significant gradient effect on the supply of ecosystem service in the Beijing Bay. In this study, nine typical ecosystem services were evaluated in the Beijing Bay using grids as the research unit, according to the biophysical processes formed by ecosystem services. Vegetation coverage and land development intensity were used to characterize gradient effect of ecosystem services, further to delineate four partitions with the dominant ecosystem service. The results showed that: 1) There was remarkable spatial variation in the distribution of ecosystem services due to the different formation process and influencing factors. Some services, such as food supply, increased from the hilly mountain to plain areas, indicating that ecosystem was greatly affected by human activity. The supply of ecosystem services, such as biodiversity, showed an opposite trend, due to ecosystem types and biophysical processes increased from flat plain to mountain. Specifically, water conservation and recreation determined the supply of ecosystem services. 2) Except recreation, most ecosystem services showed obviously gradient effects with vegetation coverage and i land development intensity. Each ecosystem service can be identified 0-2 mutation points along the change of two factors. In vegetation coverage, the mutation points of ecosystem services were 0.45-0.56, whereas in the intensity of land development were 15%-31%. Food supply and water quality regulation revealed a dramatic decrease as the increase in vegetation coverage between two identified mutation points. Water retention, quality regulation of air and soil increased significantly with the increase of vegetation coverage below the one identified mutation point. Carbon storage and erosion control constantly increased as the increase in vegetation coverage. Biodiversity enhanced remarkably with the increase of vegetation coverage between two identified mutation points. Food supply and water quality regulation showed an increasing trend with the improvement of land development intensity. Other ecosystem services continuously showed a significant downward trend with the increase in the intensity of land development. There was no mutation in water retention, carbon storage, erosion control and soil quality regulation with land development intensity. 3) Using the mutation points of vegetation coverage and land development intensity, the transitional zone of Beijing Bay was divided into four ecological regions, where the vegetation coverage of 0.45 and 15% intensity of land development. Natural or near natural region was dominated by regulation services, whereas the artificial area was dominated by supply services. Both semi-natural and semi-artificial regions were dominated by regulation and supply services, with an emphasis on a certain transitional feature. An optimized strategy of ecosystem services was proposed, according to the characteristics of different ecological regions. The findings can provide a sound basis for ecological protection, ecological restoration, and compensation policies, further to promote the sustainable development of local ecosystems.