Abstract: Miyun Reservoir is located in the East Asian-Australasian flyway． The reservoir is a habitat and feeding ground for birds, ecologically important in biodiversity conservation． At the present, little is known about the diversity of birds in Miyun Reservoir． Bird observation data platforms are used to examine bird diversity in Miyun Reservoir, to provide information for conservation and monitoring of bird resources． The composition and diversity of birds in Miyun Reservoir were studied from January 2020 to December 2022 using the point-count sampling method. A total of 20 orders, 65 families and 324 species of birds were recorded, accounting for 62.4% of the recorded bird species in Beijing． Out of these birds, 14 species are Nationally First-Grade Protected Animals and 53 species are Nationally Second-Grade Protected Animals． Passage migrants, residents, summer visitors and winter visitors accounted for 38.9%, 13.6%, 28.7% and 16.4% of the total respectively． From 2020 to 2022, no significant differences were found in bird species richness (P = 0.591), Shannon-Weiner index (P = 0.995), Pielou index (P = 0.806) and Simpson index (P = 0.144)． Species composition and diversity of bird species continued to remain stable during those 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 index 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 summer after peak spring migration, proportion of each bird species is relatively balanced． The highest value of Simpson index appears in autumn, when birds are migrating． 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 therefore is rich in bird resources and has important biodiversity protection value． It is necessary to strengthen ecological and environmental protection, to carry out bird habitat restoration work, to establish long-term and stable ecological beaches, and to continue to carry out ecological restoration research and conservation effectiveness assessment, for effective protection and management of bird diversity．