The two-component system （TCS） FlrBC mutant strains ΔflrB and ΔflrC were constructed via homologous recombination using Aeromonas hydrophila ZYAH72 as the wild-type strain. Then，differences in polar-flagellum synthesis，swimming motility，biofilm formation，exopolysaccharide secretion，adhesion ability and the resistance against whole-blood killing of the above strains were compared to investigate the function of FlrBC in A. hydrophila. The results showed that similar to the wild-type strain，both ΔflrB and ΔflrC could form polar flagellum，and there was no significant difference in swimming motility. However，crystal violet staining test revealed that the biofilm formation capacity of ΔflrB and ΔflrC decreased by 27.2% and 22.3%，respectively. The result of Congo red test showed that compared with the wild-type strain，the exopolysaccharide secretion of ΔflrB and ΔflrC decreased by 18.4% and 14.2%，respectively. The qRT-PCR results showed that the deletion of flrB and flrC inhibited the gene expression of flagellar synthesis and biofilm-related pathway. After co-incubation with grass carp CIK cells，the adhesion rate of ΔflrB and ΔflrC decreased by 23.2% and 18.2% respectively compared with the wild-type strain. The results of whole blood killing assay showed that the ability of ΔflrB and ΔflrC to resist whole blood killing was significantly reduced. The above results show that TCS FlrBC is not required for the formation of polar flagella in A. hydrophila，but plays a regulatory role in bacterial flagella assembly and biofilm formation，and affects the pathogenicity of A. hydrophila.