As one of the most likely substitutes for conventional antibiotics,antimicrobial peptides ( AMPs) are ancient players in innate immunity. In the antimicrobial action of AMPs,an initial key event is that AMPs firstly contact with and then closely adhere to the bacterial membrane. In order to reveal this unknown process,a molecular dynamic ( MD) simulation is performed to examine the nonspecific interaction of AMP HP( 2-20) with the cell membrane,which is modeled by a POPE bilayer. The results show that the N-terminal of the peptide firstly contacts with the membrane,and then,companying with a rotation movement,the peptide slowly inclines toward and slightly inserts into the membrane; at the same time,the AMP limits the movements of the lipids adjacent to the peptide,which induces the membrane to become non-uniform and enhances the irregular fluctuation of the lipids, so that other peptides may find their chances of deeply inserting into the membrane.