Abstract: Objective To explore the different effect of elafin incubated by different bacteria on P.aeruginosa(Pa) bioflim. Methods To cultivate the A549 cells in vitro, the pEGFP-N1-elafin eukaryotic expression vectors have been transfected to the cells by LipofectamineTM 2000. Elafin transfected cells incubated by the supernatant of S. epidermidis (S.epidermidis group), Pa (Pa group) and E.coli (E.coli group) respectively 24 hours，the A549 cells were transfected the vector without elafin gene as normal group. Then the levels of elafin were detected by ELISA and Western Blot. To establish the Pa biofilm model in vitro，a rapid silver nitrate staining procedure and scanning electronic microscope (SEM)demonstrated bacterial biofilm. After biofilm carriers put into each group and incubated 8 hours, we measured the proportion of bacteria biofilm by silver nitrate staining in light mocroscope and observed the structure of biofilm by SEM in each group. Results The Pa and E. coli groups（especially Pa） induced the content of elafin in cells and the level of secretion increasing compared to the normal group, while the S. epidermidis group have no increase. Both silver nitrate staining procedure and SEM demonstrated bacterial biofilms. The the proportion of bacteria biofilm and the structure of BF in Pa and E. coli groups were changed, especially in Pa group. Conclusions There was specificity of different bacteria to induce the express of elafin. The inducing effect of Pa were exceed that of E.coli, S. epidermidis had厮 no obvious effect. Elafin could clean the bacteria of biofilm.