Abstract: Rapid quantitative detection of aquatic animal pathogens helps to achieve early warning and accurate diagnosis of aquatic diseases. A pathogenic Halomonas 7T strain isolated from a larval pond of Crossostrea gigas in the North Yellow Sea was studied.Specific primers were designed based on the sequence of its chaperone protein Dnak coding gene, and the strain could be detected from environmental samples. The plasmid was constructed by TA cloning, and the quantitative detection of the strain was realized by real-time quantitative PCR.