[Objective] The dynamics of water-related ecosystem services and its influences by south-to-north water diversion project were analyzed, in order to protect water resources and ecosystem balance of Miyun Reservoir. [Methods] The methods of market value, alternating engineering, alternative cost, carbon trading, willingness to pay, proportion apportionment and benefit transfer were used to evaluate the water-related ecosystem services of water resources supply, aquatic product provision, flood regulation and reservation, air humidity improvement, summer heat amelioration, water purification, water conservation, CO₂ sequestration, O₂ release, biodiversity protection, tourism and leisure and scientific research and education of Miyun Reservoir. [Results] The water-related ecosystem service values of Miyun Reservoir ranged from 70.996 to 100.360 billion during 2008—2019, which fluctuated slightly at first and then increased. As for components of water-related ecosystem services, the value of supporting services, especially biodiversity protection, played a dominant role (64%~80%). The value of regulating services was in the secondary position (18%~33%), which was mainly manifested in water conservation, humidity improvement, summer heat amelioration and flood regulation and reservation. The value of provisioning services and cultural services together accounted for less than 5%. Moreover, the south-to-north water diversion project significantly increased the values of air humidity improvement, summer heat amelioration, water conservation, water purification, tourism and leisure, scientific research and education and total ecosystem services (p<0.01), while significantly decreased the value of flood regulation and reservation (p<0.01). [Conclusion] The water ecological service function of Miyun Reservoir is affected not only by natural factors such as climate, but also by human factors such as south to north water diversion project and traffic convenience. The monitoring of water volume and quality and the development of cultural and ecological potential of Miyun Reservoir should be strengthened, so as to guarantee the security and reliability of drinking water reserves for Beijing City.