Abstract: To investigate the spatial distribution patterns of species diversity and functional feeding groups of benthic macroinvertebrates in the Nemoer River, a key river in western Heilongjiang Province, and to further enrich the regional dataset on functional ecology of benthic macroinvertebrates, a systematic survey was conducted from September to October 2022 at 16 sampling sites along the main stream of the Nemoer River. The study examined community composition, species diversity, and functional feeding group structure of benthic macroinvertebrates, and applied the functional feeding group evenness index (j_FD) to assess the ecological health status of the river. The results showed that a total of 61 taxa of benthic macroinvertebrates were identified during the survey, belonging to 6 classes, 15 orders, 38 families, and 53 genera/species. Aquatic insects dominated the community, comprising 40 species (65.6% of the total number of taxa). The dominant species included Koreoleptoxis amurensis, Potamyia sp., Baetis sp., Heptagenia sp., and Orientogomphus sp.. In autumn, the Shannon-Wiener diversity index, Pielou evenness index, and Margalef richness index of benthic macroinvertebrates in the Nemoer River ranged from 1.04 to 3.78, 0.64 to 0.97, and 0.58 to 4.23, respectively. These three indices showed no significant spatial differences among the upper, middle, and lower reaches (p>0.05). However, the community composition of benthic macroinvertebrates exhibited highly significant spatial variation (Global R=0.83, p<0.01). In terms of functional feeding groups, benthic macroinvertebrates in the Nemoer River during autumn comprised 23 predator species, 10 collector-gatherer species, 10 filter species, 9 scraper species, and 9 shredder species. Among these, scrapers had the highest relative density, while shredders had the lowest. The assessment based on the functional feeding group evenness index (j_FD) showed that the average j_FD value across all sampling sites was 0.74, indicating that the functional structure of the benthic macroinvertebrates community in the main stream of the Nemoer River remains highly balanced and that the ecosystem is generally in good health. This study can provide a scientific basis for assessing aquatic biodiversity, environmental monitoring, and formulating management strategies for key rivers in Heilongjiang Province, and also offers practical reference for evaluating ecosystem health in seasonal rivers of northern China.