In this study， we identified the important fish pathogenic bacterium， Edwardsiella piscicida， GadBCD， the strong acid resistance system and its function. Sequence analysis and co-transcription experiments showed that the GadBCD system consists of one glutamic acid decarboxylase， one glutaminase and three transporters， which form a manipulator. qRT-PCR revealed that gadBCD expression was largely unchanged upon strong acid and high temperature stimulation of bacteria， but significantly up-regulated upon hydrogen peroxide and host serum stimulation. A GadBCD system deletion mutant strain ΔgadP was constructed using homologous recombination， and experiments comparing the growth curve and survival rate under acidic stress of wild strain and ΔgadP revealed that the GadBCD system is not only an important player in the resistance of E. piscicida to medium to strong acids， but is also required for resistance to strong acids. GadBCD was found to be involved in bacterial virulence by comparing wild strain and ΔgadP in terms of biofilm formation， motility， resistance to host serum killing， and infection of cells. In conclusion， the GadBCD system is an important strong acid resistant system of E. piscicida and is involved in bacterial pathogenesis.