In order to define the potential pathogens causing fulminant illness of Procambarus Clarkii in Dangtu County, Anhui Province, pathogens were isolated from the moribund Procambarus Clarkii. A dominant strain named XLX1 was isolated from the hepatopancreas and was confirmed to be pathogenic to Procambarus Clarkii by artificial challenge test. The XLX1 isolate was identified as Citrobacter freundii by means of the morphology, physiological and biochemical characteristics and 16S rRNA gene sequencing. The antibiotics sensitivity, adhesin-carrying genes and cell adhesion of XLX1 isolate were further detected. The results showed that the XLX1 isolate was sensitive or medium sensitive to cefotaxime, gentamicin, amikacin, neomycin sulfate, enrofloxacin, norfloxacin and teicoplanin, but resistant to other 7 kinds of antibiotics. The XLX1 isolate carried adhesin genes cfa and ure clusters. It was found that ureABC structure gene and ureD key accessory gene was relatively conservative by the sequences analysis. The nucleotide and amino acid homology of former respectively ranged from 93.2% to 98.3% and 91.7% to 97.4%, and the latter ranged from 90.8% to 98.3% and 94.7% to 98.7% between XLX1 isolate and reference strains. Compared with reference strains derived from patient, the 294th, 600th, 608th amino acids in UreABC structure protein and the 62 nd and 122 nd amino acids in UreD key accessory protein generated sense mutation amino acids from XLX1 isolate. XLX1 isolate adhered to the epithelioma papulosum cyprinid(EPC) cells mainly in aggregative pattern, and the average adhesive bacterial number was 29.8±5.3, which caused EPC cells lesion with the extension of adhesion time. This study may contribute to providing a theoretical basis for controlling aquatic animal disease caused by Citrobacter freundii.