Abstract: Phytoplankton is the hub of energy flow and material cycle in aquatic ecosystems, and their interspecific relationships profoundly impact community assembly and ecological function. However, the key mechanisms driving the coexistence and stability of dominant species in the Qinghai-Xizang Plateau rivers with extremely high environmental heterogeneity are still unclear. In order to reveal the relationship among dominant phytoplankton species in typical rivers of Xizang, this study collected phytoplankton samples from 47sections of 14 typical rivers such as the Yarlung Zangbo River, Nujiang River, and Lancang River from August to September 2024. Based on the multi-index coupling of niche breadth (Levins index), niche overlap (Pianka index) and interspecific association (χ², AC, Pearson), the niche characteristics and interspecific relationships of dominant species were analyzed. A total of 71species of phytoplankton were identified in this survey, and 16 dominant species were screened out, with a dominance of 62%. Navicula sp., Synedra sp., and Cymbella sp. had the largest niche breadths, while Hydrurus foetidus had the smallest, showing a ‘wide-narrow’ niche coexistence pattern. The average niche overlap value of the 120species pairs was 0.36, and 38.33% of species pairs had an overlap<0.25, reflecting a coexistence strategy of ‘overall differentiation and local overlap’. The overall community showed a significant positive association (VR=2.47, W=113.76, P<0.05), and the ratio of positive and negative association was 2.24. The Pearson correlation coefficient was significantly positively correlated with niche overlap value and niche similarity (P<0.001). Based on canonical correspondence analysis (CCA), dissolvedoxygen, pH, water temperature, and conductivity were the key environmental factors driving the distribution of phytoplankton dominant species (P<0.05). In summary, phytoplankton in typical rivers in Xizang through ‘niche differentiation-positive association’.