Abstract: Miyun Reservoir is located in the East Asian-Australasian flyway, and is a habitat and feeding ground for birds, which is ecologically important in biodiversity conservation, but there is a lack of research on the diversity of birds in Miyun Reservoir at present. This study is based on bird observation data platforms to carry out a study of bird diversity in Miyun Reservoir and to provide basic information for the conservation and monitoring of bird resources in China. The study on the composition and diversity of birds in Miyun Reservoir was conducted from January 2020 to December 2022 using the point-count sampling method. The results showed that 20 orders, 65 families and 324 species of birds were recorded, accounting for 62.4% of the recorded bird species in Beijing. Among them, there are 14 species of Nationally First-Grade Protected Animals and 53 species of Nationally Second-Grade Protected Animals; Passage migrants, residents, summer visitors and winter visitors accounted for 38.9%, 13.6%, 28.7% and 16.4% respectively. Between 2020 and 2022, there were no significant differences in bird species richness (P=0.591), Shannon-Weiner index (P=0.995), Pielou index (P=0.806) and Simpson index (P=0.144) in the Miyun Reservoir, and the species composition and diversity of the bird species continued to remain stable during the three years. The highest values of the Shannon-Weiner index all occurred in summer, indicating that the Miyun Reservoir is rich in food sources in summer, providing suitable habitat for birds. The Pielou indices for the summers of 2021 and 2022 were significantly higher than those for the other three seasons, indicating that the bird community structure tended to be stable in the summer after the peak of spring migration, and the proportion of each bird species is relatively balanced. The highest value of Simpson index appears in autumn, when birds are migrating. At this time, the number and relative abundance of winter visitors such as Bean goose, Daurian Jackdaw and Ruddy Shelduck are increased, thereby raising the Simpson index. Miyun Reservoir is rich in bird resources and has important biodiversity protection value. It is necessary to strengthen ecological and environmental protection, carry out bird habitat restoration work, establish long-term and stable ecological beaches, and continue to carry out ecological restoration research and conservation effectiveness assessment, so as to provide a basis for effective protection and management of bird diversity.