Abstract: Understanding the seasonal dynamics of suspended particulate matter (SPM) and the response mechanism of the attached bacterial community in Changdang Lake is crucial for clarifying the ecological effects of the "particulate matter-microorganism" interaction in overwater shallow lakes under hydrological fluctuations. In June, August and November 2024, the temporal and spatial variation characteristics of SPM particle size and water ecological environment indicators, as well as the attached bacterial community of SPM in Changdang Lake, were analyzed. The results showed that the median particle size (D₅₀) of SPM in June, August and November ranged from 7.81 to 10.45 μm, 651.83 to 884.75 μm, and 6.92 to 48.52 μm, respectively. The overall average chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), total nitrogen (TN) and total phosphorus (TP) in Changdang Lake met the surface water quality standards of Class IV. Correlation analysis indicated that D₅₀ was positively correlated with NH₄⁺-N (P < 0.05) and negatively correlated with DO and pH (P < 0.01). There were 10 phyla with a proportion greater than 1% in SPM. Among them, Proteobacteria was the highest (29.8%), followed by Cyanobacteria (28.34%) and Bacteroidota (15.69%). Phenylobacterium, HgcI clade and Comamonas were the key species in the network. Among the nitrogen cycling functional genes, DNRA (dissimilatory nitrate reduction to ammonium) genes were dominant, followed by nitrification genes, while the abundance of nitration-related genes was relatively low, indicating that the synthesis of proteins by algae using nitrate plays a dominant role in the nitrogen cycling of the water body in Changdang Lake. The research results provide theoretical basis and technical support for the restoration of water transparency and the regulation of microbial functions in eutrophication control.