[Objectives] Research on elevational diversity patterns of birds has always been an important subject in the ecology of bird communities. Seasonal change was thought to influence the elevational diversity patterns of bird communities in the mountainous regions. The bird diversity of Gongga Mountains is abundant, but research on seasonal diversity change is still insufficient. Therefore, our study aims to understand the seasonal changes of elevational diversity pattern of birds at the eastern slope of Gongga Mountains. [Methods] We mainly used line transect method to survey the bird diversity in every 400 m elevational band between 1 200﹣4 400 m at the eastern slope of Gongga Mountains (Fig. 1) in breeding seasons (March to June in 2012, 2017, 2018 and March to May in 2016) and non-breeding seasons (September to October in 2012 and November to December in 2017, 2018). We added up all resident/migration types of species numbers and individuals in the breeding and non-breeding seasons every 400 m elevational bands from 1 200﹣4 400 m, then calculated the Shannon-Weiner diversity index, Simpson’s diversity index, Pielou evenness index, Berger-Parker dominance index (alpha diversity), Cody diversity and Bray-Curtis dissimilarity index (beta diversity). We furthermore used the Cody diversity index of the birds’ community and species richness of plant community at each elevational band to calculate their Spearman correlation. We defined dominant species by the percentage of all individual numbers at every 400 m elevational bands during the breeding and non-breeding seasons to check whether these dominant and common species shifted their elevational distribution during the breeding and non-breeding seasons. [Results] 1. Our results show that 36 species of summer visitors reduced during the non-breeding seasons, and the component of dominant species changed significantly during the breeding and non-breeding seasons except for middle elevations (Table 1). 2. There were 4 types of elevational distribution shifts, including a downward shift during the non-breeding seasons, wider distribution during the breeding season than non-breeding seasons, wider distribution during the non-breeding seasons than breeding seasons, and no shifts happened during both seasons. Besides there were more omnivores than insectivores which had wider elevational distribution during the non-breeding seasons than breeding seasons (Fig. 2). 3. Species richness and abundance were highest during the breeding seasons at 2 000﹣2 400 m and during the non-breeding seasons at 1 600﹣2 000 m. The Shannon-Weiner index and the Simpson’s index had a similar pattern, both were unimodal with the highest value at 1 600﹣2 000 m during the breeding seasons, and bimodal with the highest value at 1 600﹣2 000 m and 2 800﹣3 200 m during the non-breeding season. The Pielou evenness index had the highest value at 3 200﹣3 600 m during the breeding seasons, but had the highest value at 1 600﹣2 000 m and 3 600﹣4 000 m during the non-breeding season. The Berger-Parker dominance index was monotonically increased with elevation during both seasons (Fig. 3). 4. The Cody diversity and Bray-Curtis dissimilarity index (beta diversity) showed similar patterns, both declined with increasing elevation, and both had the lowest beta diversity at 3 600﹣4 400 m (Fig. 4 and Fig. 5). Besides, the Cody diversity index had a significantly positive correlation with the elevational diversity of plant community. [Conclusion] The diversity hotspot of birds during the breeding seasons was located at the middle elevations, while it occurred at both low-middle and middle-high elevations during the non-breeding seasons. This seasonal diversity change caused by the migration of birds and the phenology of plants has important impact on the elevational α-diversity patterns of birds. On the other hand, although the seasonal temperature change in the Gongga mountains is significant, the elevational β-diversity patterns of birds during the breeding and non-breeding seasons were relatively stable. This phenomenon has an extremely significant positive correlation with the elevational diversity of plant community, which demonstrate that the component of plant species at each elevational vegetation zones is probably an important factor for the β-diversity pattern of birds. The significant difference of elevational diversity patterns of bird communities in different seasons indicates that we need to pay more attention to the changing of bird diversity, controlling the human activities and protecting the habitats for birds in different seasons in mountainous areas in future diversity research and conservation management.