Pennisetum centrasiaticum is a perennial grass that exhibits a broad distribution in the upper and middle reaches of the Yarlung Zangbo River. It can provide forage for animals and has high ecological value. In this study, 26 communities of P. centrasiaticum were chosen, and an examination of phenotypic characteristics and environmental variables was conducted to explore the phenotypic diversity of P. centrasiaticum germplasms and determine the climatic factors that affect its growth. Results showed that Mainling County had the lowest altitude of the sampling site, measuring 2883 m, whereas Gamba County had the most significant altitude of the sampling site, measuring 4567 m. The analysis of phenotypic features in P. centrasiaticum indicated a significant abundance and diversity of germplasms within the Yarlung Zangbo River Basin. Strong correlations were observed between climatic factors and phenotypic traits, suggesting a close relationship between the growth characteristics of P. centrasiaticum and the environment. Precipitation was significantly positive correlated with plant height (r=0.51), Number of above-ground internodes (r=0.72), ear length (r=0.54), ear width (r=0.66), and dry weight (r=0.65), which increased biomass production of P. centrasiaticum. As altitude climbed, plant height, stem diameter, heading rate, and dry weight decreased, whereas the ratio of the last internode increased. A principal component analysis was performed on 12 phenotypic variables of P. centrasiaticum. These qualities were categorized into three primary components, accounting for 81.13% of the total contribution. This research concludes that the Yarlung Zangbo River Basin exhibited a significant morphological variation in P. centrasiaticum germplasms. Altitude and precipitation caused phenotypic changes of P. centrasiaticum in the upper and middle reaches of the Yarlung Zangbo River. The germplasms obtained from this region can potentially expedite the use of indigenous grass species in mitigating soil erosion, safeguarding ecological integrity, and facilitating forage breeding on the Tibetan Plateau.