Abstract: In order to explore the cause of death of a dead Chinese sturgeon, firstly, the body surface observation, pathological anatomy and clinical diagnosis of the dead Chinese sturgeon were performed, and then the histopathological observation of the dead Chinese sturgeon was performed through histopathological slides and H.E. staining. The results showed that the dead Chinese sturgeon had black body color, red and swollen anus, and the gill filaments were comb toothed and the ends were dark brown. After dissection, the liver showed congestion and necrosis, which was dark brown. The stomach was severely enlarged and hard, with a thick stomach wall, and there was no food inside. After being opened, a large number of foreign bodies wrapped in light yellow mucus were found, which were examined as biological filter materials in the mobile bed of the circulating aquaculture system. The kidneys were necrotic and numerous black blood clots were seen between the tissues. Histopathological observation showed that there were a large number of inflammatory cells or red blood cell infiltration between cells in liver, kidney, intestine and stomach. Coagulation necrosis occurred in hepatocytes, intercellular lipofuscin deposition, serious damage to bile duct, necrosis and shedding of tissue cells. The glomeruli were enlarged and mesangial proliferation; the basement membrane of the renal tubules was separated; the epithelial cells were loosely arranged; the renal tubules were atrophied, and the interstitial fibrosis was proliferated. The serosa and muscle layer of the intestinal tract were partially exfoliated; the columnar epithelial cells of the mucosal layer were necrotic and exfoliated, and a small amount of necrotic and exfoliated intestinal tissue cells were distributed in the intestinal cavity. The columnar epithelial cells of the gastric mucosa were separated from the lamina propria. These results indicated that the dead Chinese sturgeon had multiple organ lesions due to ingestion of biofilter material in recirculating aquaculture system, which eventually led to death.