Periphytic algae is an important primary producer in the river ecosystem, and it is one of the important indicators for the monitoring and evaluation of river water ecology. As a typical plateau river, the assembly process of the algae community in the Yarlung Zangbo River is still unclear. In May 2022 and July and September 2023, algae samples were collected, and water environmental factors were determined in the lower reaches of the Yarlung Zangbo River. The algal species were identified, and cell abundance and biomass were calculated using in vivo observation and fixed staining techniques to explore the diversity pattern of algae communities in the lower reaches of the Yarlung Zangbo River, to clarify the relative importance of deterministic and random processes in the assembly of algal communities, and to reveal the influencing factors driving the assembly process. The results showed that there were significant differences in the time of water environmental factors, mainly concentrated between spring, summer, summer, and autumn. A total of 274 species of algae were identified in the three seasons, belonging to 7 phyla, 9 classes, 18 orders, 31 families, and 63 genera, and the community differences between seasons were significant （