[Objectives] The determinant of biodiversity maintenance of natural communities is important in ecological research. In this study, we aim to survey the bird species diversity of Bita Lake-Shudu Lake region of Potatso National Park, and further explore the functional trait diversity pattern and the underlying mechanism of the wintering bird communities of this region. [Methods] We used line transect method in this study from August 2021 to July 2022. Specifically, eight transects with a total of 17 km long were selected in Bita Lake-Shudu Lake region of Potatso National Park. Besides, we set up twenty-four infrared cameras from November 2021 to October 2022 to obtain bird species diversity in this region. From November 2021 to March 2022, we surveyed bird composition of 30 wintering bird communities belongs to four habitat types:plateau lakes, alpine meadows, mixed coniferous and broad-leaved forests, and coniferous forests in the region (Fig. 1 and Appendix 1). We selected 15 functional traits of bird in the database (Appendix 5), including four morphological traits (mass, beak width, wing length, tail length) (Appendix 2), six traits of diet (vertebrate, invertebrate, scavenger, nectar & fruit, seed, plant), and five traits of foraging strata (canopy or aerial, midhigh, understory, ground, water). Based on bird functional traits, functional richness (FRic) is used to measure the volume of functional space, and mean nearest neighbor functional distance (MNND) is used to measure species distribution in functional space, then use “Picante” package in R to build unconstrained null model and constrained null model by using “independentswap” method. The standardized effect size (SES) generated by the null model was used to infer the dominant drive mechanism of wintering bird community assembly. Finally, the paired t-test was used to compare whether the functional richness (FRic) and mean nearest neighbor functional distance (MNND) of the community were significantly different before and after the removal of wintering birds, and then combined with the null model results to explore the influence of wintering bird community on the functional structure. [Results] A total of 114 bird species belong to 13 orders, 42 families were recorded, 74 birds have been added to the previous field record of this region (Appendix 6). Five and fourteen species were listed as National Class I (Appendix 7) and II protection bird in China respectively. The four habitat types held different bird species composition, with overlap for the two forest habitat types (Fig. 2), however, there is no complete overlap in the survey points. Sixteen wintering birds recorded in plateau lakes and alpine meadows significantly expanded the functional trait space of the community (P < 0.05), meanwhile significantly reduced the mean nearest neighbor functional distance (P < 0.05) between species in the functional space (Fig. 4). The functional richness of the wintering bird community increased with the increase of species richness (Fig. 3), but the null model analysis found that the observed functional richness was generally smaller than expected (Fig. 5), that is, the functional space increased with the increase of species richness, but its increase was limited by environmental filtering. The mean nearest neighbor functional distance of species in functional space became closer with the increase of species richness (Fig. 3), while the constrained null model showed that the standardized effect size was almost greater than zero (Fig. 6), in other words, with the increase of species richness, species are packed more closely in the functional space, but limited by the effect of limiting similarity, species will not gather indefinitely. [Conclusion] This study updated field records of bird species of the Bita Lake-Shudu Lake region of Potatso National Park, which can provide a new data basis for the conservation and management of bird diversity in the region. The migration of wintering birds filled the gap of niche and made the functional structure of wintering bird community more compact and stable. More importantly, our results showed that the functional space of the wintering bird communities was constrained by environmental filtering, meanwhile, the distribution of bird within the functional trait space was affected by the limiting similarity, that is, environmental filtering and limiting similarity are doubly important for wintering bird community assembly.