The study of phylogeny and functional trait structure of plant communities is crucial for understanding mechanisms of species coexistence and biodiversity maintenance. The gradient of slope positions compresses factors such as elevation and topography within a limited vertical geographic space, thereby influencing the distribution, structure, and functionality of plants. This study focuses on the plant communities at different slope positions in the subalpine meadows of Gannan. By integrating environmental factors, community surveys, and functional trait measurements, we calculated the Net Relatedness Index (NRI), Nearest Taxon Index (NTI), and standardized effect size of the Mean Pairwise Trait Distance (SESMPD) to analyze changes in phylogenetic and functional trait structures along the slope gradient, revealing species coexistence mechanisms in Gannan's subalpine meadows. The results showed that: (1) Species richness, Shannon-Wiener index, and phylogenetic alpha diversity significantly decreased with increasing slope position (P<0.05), while species evenness did not show a significant change (P>0.05); (2) The overall phylogenetic structure was aggregated (NRI>0, NTI>0), and the coexistence of community species was mainly dominated by habitat filtration, and the NTI index showed a 'V’-shaped change, indicating that habitat filtration weakened and then strengthened with the increasing of slope position, and the degree of aggregation of community phylogenetic structure likewise weakened first and then strengthened; (3) Functional trait structure shifted from a dispersed state (SESMPD<0) in the flat and lower slope position to an aggregated state (SESMPD>0) in the middle and upper slope position, with pronounced species interactions from flat to lower slope position and a predominance of environmental habitat filtering from middle to upper slope position; (4) Of the seven plant functional traits examined, only leaf carbon content and leaf phosphorus content showed significant but weak phylogenetic signals (P<0.05), suggesting that evolutionary history had a minor influence on the plant communities in the study area, and that phylogenetic and functional trait patterns were not entirely consistent. In summary, niche determinism was the primary mechanism for species coexistence along the slope gradient in Gannan's subalpine meadows. Soil moisture was a relatively important environmental factor regulating the functional trait structure of plants at different slope positions. As soil moisture decreased, the functional trait structure shifted from divergence to aggregation. This study provides a more substantial theoretical basis for the mechanisms of species coexistence in the subalpine meadows of Gannan Prefecture.