To perform pathogenic and pathological investigations on explosive epidemics of Hyriopsis cumingii Lea in Hunan Province, China between 2005 and 2011. We isolated pathogenic bacteria SJ-2 from naturally infected Hyriopsis cumingii Lea, and the SJ-2 strain was artificial infected into the normal Hyriopsis cumingii Lea by axe foot injection method. The strain was identified according to conventional bacteriological isolation and identification and molecular biology methods, and pathological changes caused by the bacteria in diseased mussel tissues were observed. According to morphological and culture characteristics, physiological and biochemical tests and 16S rDNA molecular identification, SJ-2 strain shares 99% sequence identity with the type strain of Aeromonas veronii (A. Veronii). Results for antibiotic susceptibility tests showed that among 50 drugs, A. Veronii was highly sensitive to 15 drugs, moderately sensitive to 5 drugs, and showed drug resistance to left drugs. Macroscopical lesions, pathological changes and cytopathology were summarized. The pathogenic bacteria SJ-2 was isolated from Hyriopsis cumingii Lea affected by explosive epidemic disease, and was identified as A. Veronii. SJ-2 strain caused multi-organ lesions and function failure in corresponding organs in the Hyriopsis cumingii Leal, resulting in gradually decreased and disappeared normal physiological metabolism, and eventually death.