Free flowing tributaries are important for maintaining of the aquatic biodiversity in dammed systems. As an important first-class tributary of the lower reaches of the Lancang River, the Buyuan River maintains a relatively natural state with little anthropogenic disturbance, serving as an important habitat for indigenous fish and aquatic organisms of the Lancang River basin. In the context of hydropower development in the basin, knowledge on the spatio-temporal distribution of macroinvertebrate community in Buyuan River and its influencing factors are of great significance to the biodiversity conservation and restoration of the Lancang River and the rivers in southern China. To address these issues, a detailed survey on macroinvertebrate in the Buyuan River was conducted in April 2019 (dry season) and October 2019 (rainy season). As a result, a total of 150 macroinvertebrate taxa were detected, belonging to 5 phyla, 7 classes and 68 families, including 121 aquatic insect species, 20 mollusca species, 3 leeches, 2 oligochaetes, 2 crustaceans, and 1 planaria and 1 nematode. Trichoptera and ephemeroptera were dominant taxa groups in the whole basin. The density and biomass of macroinvertebrate species in the upper reaches of Buyuan River were higher than those in its middle and lower reaches in both the dry and rainy seasons. The species richness and the Shannon-Wiener diversity index was significantly higher in the rainy season than in the dry season. Among the functional feeding groups, the filter-collectors (41.09%) and gather-collectors (31.81%) dominated, followed by the scrapers (11.00%), predators (11.21%) and shredders (4.89%). Mantel test showed that river width (RW), NO₃^--N and chemical oxygen demand (COD_Mn) were the main environmental factors affecting the diversity of macroinvertebrate fauna in Buyuan River. Meanwhile, different functional feeding groups were affected by different environmental factors. The evaluation of biological index and biological monitoring working party showed that most sample sites in Buyuan River were at the good level and above (only a few sites as medium level and below), and the overall water ecological condition was good.