[Background] The disease, causing fulminant hemorrhagic of yellow catfish (Pelteobagrus fulvidraco), occurred in a pond in Dangtu County, Anhui Province, and the pathogen is controversial currently. [Objective] Investigate the pathogen causing outbreak hemorrhagic disease of yellow catfish (Pelteobagrus fulvidraco) and the biofilm formation characteristics of the isolated strain, to provide a reference for the prevention and treatment of A. jandaei infection. [Methods] The organs with obvious pathological changes in dying yellow catfish were inoculated on the EPC cell and media (TSB agar plate and blood agar plate) to isolate the pathogen, and the pathogenicity of the isolate was detected by artificial infection test. The isolated strain was identified by phenotypic identification and 16S rRNA gene sequence analysis. Then, the optimal conditions for biofilm formation, biofilm forming ability of the isolated strain and biofilm-forming genes carried by the strain were detected. [Results] A dominant isolated strain named HSY-2 was recovered and purified from organs with obvious pathological changes. In the artificial infection trail, the bacterial isolate HSY-2 exhibited virulence to yellow catfish with an LD50 value of 1.05×106 CFU/mL. The bacterial isolate was identified as Aeromonas jandaei according to morphology, biochemical characteristics and phylogenetic analysis derived from 16S rRNA gene. The optimum condition for forming biofilm was to inoculated on the TSB medium for 96 h at 30 °C, at which the isolated strain might form a moderate intensity biofilm. Three biofilm formation related genes, including glycerol-3-phosphate dehydrogenase D gene glpD, S-ribosylhomocysteine lyase gene luxS and LuxI family protein homolog gene ahyI were detected in the isolated strain, whereas the mannose-sensitive hemagglutinin pili biosynthesis protein Q gene was not detected. [Conclusion] This experiment provides a basis for further study on the regulation mechanism of A. jandaei biofilm formation and a reference for the prevention and treatment of A. jandaei infection from the perspective of anti-biofilm formation.