In order to explore the expression characteristics and protein function of vstm2a gene in response to bacterial infection in Cynoglossus semilaevis， in this study， the relative expression characteristics of vstm2a in immune tissues （gill， liver， spleen， intestine and kidney） of Cynoglossus semilaevis after infection with Vibrio harveyi， Vibrio anguillarum， Vibrio alginolyticus， Edwardsiella tardaand Streptococcus agalactiae were detected by real-time fluorescence quantitative PCR （RT-qPCR）. The prokaryotic expression recombinant plasmid of vstm2a gene was constructed and the recombinant protein was obtained. The Oxford cup method， bacterial protein binding experiment and siRNA silencing were used to explore the function of vstm2a protein in bacterial invasion. The results showed that the vstm2a protein had a transmembrane domain and an Ig domain， which functions on the cell surface ；The expression of vstm2a gene in related immune tissues was significantly increased at 6 h， 48 h and 72 h after infection with Vibrio harveyi， Vibrio anguillarum， Vibrio alginolyticus， Edwardsiella tarda and Streptococcus agalactiae. After incubation with bacteria， the vstm2a recombinant protein was co-precipitated with bacteria by low-speed centrifugation. Bacteriostatic experiments showed that it significantly inhibited the growth of bacteria， and after siRNA reducing the vstm2a gene， it inhibited the expression of cytokines IL-6 and IL-10. This study demonstrates that vstm2a protein can respond to bacterial invasion， recognize and bind bacteria， and play an immune defense role against pathogen infection by inhibiting bacterial growth and activating pro-inflammatory cytokines. It is an important immune protein. This study is helpful to analyze the mechanism of bacterial adhesion to cells or fish resistance to bacterial invasion， and provides a theoretical basis for the future selection of resistant varieties by molecular means.