Abstract: This study focuses on the bactericidal effect of cold nitrogen plasma on Escherichia coli O157∶ H7( E.coli O157∶ H7)biofilms formed on fresh cucumber.The results of the vitro experiment demonstrated that plasma has a satisfactory eradicating effect on E. coli O157 ∶ H7. After exposure to plasma at 500 W for 4 min,almost 99.99% and 99.21% reductions in E. coli O157∶ H7 populations were achieved in vitro and on cucumber,respectively. Confocal laser scanning microscopy( CLSM) was adopted to detect the bacterium community quantity unit area and thickness of bacterium biofilms.Scanning electron microscope( SEM) was used to observe surface structure of biofilms.In conclusion,plasma was an effective method on eradicating biofilms and simultaneously had mild effect on sensory quality of fresh cucumber.