Understanding the mechanisms of competition and coexistence among sympatric species is crucial for deepening our understanding of interspecific interactions and informing the conservation of rare and endangered wildlife. In this study, we utilized DNA macro-barcoding technology to analyze the seasonal dietary habits of Kiang (Equus kiang) and Tibetan Gazelle (Procapra picticaudata) in Shiqu County, Sichuan Province, aiming to investigate their resource partitioning strategies and potential competition for limited forage resources. The results showed that Kiang mainly consumed Cyperaceae and Polygonaceae in both seasons, while Tibetan Gazelle fed on Polygonaceae and Rosaceae in the warm season and shifted to Ephedraceae in the cold season. Both species exhibited significant seasonal differences in dietary composition, with Tibetan Gazelle showing greater individual variation and seasonal shifts. In addition, their dietary niche was broader in the warm season, and overlap remained high, with indices of 0.89 and 0.87 in the warm and cold seasons, respectively. The results indicate that although Kiang and Tibetan Gazelle exhibit partial dietary overlap, they mitigate interspecific competition and achieve sympatric coexistence through differential use of dominant forage species and adjustments in dietary proportions. This study highlights a competition–coexistence dynamic along the trophic niche axis in typical plateau ungulates, providing insights for effective conservation strategies and biodiversity conservation in plateau regions.