Quorum sensing (QS) is a communication pattern between bacteria， hence the inhibition of bacterial QS system could be used as a new strategy to the control the spoilage caused by bacteria， and to some extent could avoid the bacteria drug resistance. In the study， dandelion water extract mediated biosynthesis Ag nanoparticles (D-AgNPs) was prepared with AgNO3 as silver source and dandelion water extract as reducing agent. Its structure was characterized by ultraviolet visible absorption spectroscopy(UV-vis)， dynamic light scattering(DLS)， Zeta potential， X-ray diffraction (XRD)， Fourier transform infrared spectroscopy (FTIR)， scanning electron microscopy (SEM) and X-ray energy spectrum(EDS). It was found that the synthesized D-AgNPs were spherical， with an average particle size of 13.9 nm and Zeta potential of (-14.07±0.25) mV. The effects of D-AgNPs on the growth of two Hafnia strains and quorum sensing regulated virulence factors such as biofilm， AHLs， proteases， exopolysaccharides， swimming and swarming motilities were determined. It was found that the minimum inhibitory concentration of D-AgNPs against Hafnia was 128 μg/mL， and could inhibit the formation of the biofilms of Hafnia at 1/16~1/2 MIC (8-64 μg/mL)， whereas promoted its biofilm formation at 1/128~1/32 MIC(1-4 μg/mL). D-AgNPs showed different inhibition abilities on the AHLs and protease production， as well as swimming and swarming motilities； however， sub-MIC D-AgNPs promoted the production of exopolysaccharides. It is proved that D-AgNPs could be used as quorum sensing inhibitor.