Antimicrobial peptides are novel biological preservatives in the food industry， and salted fermented foods are one of the sources of antimicrobial peptides (AMPs). In this study， ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) was used to identify small molecule peptide sequences from salted Penaeus vannamei， and potential antimicrobial peptides were analyzed and screened by bioinformatics. Antibacterial activity and mechanism of AMPs against Vibrio parahaemolyticus were evaluated by minimum inhibitory concentration， time-kill curve， cell membrane permeability， and circular dichroism. The results showed that the minimum inhibitory concentration of the novel AMP (PV-M7) from salted Penaeus vannamei was 15.6 μg/mL against Vibrio parahaemolyticus， and the antibacterial activity was exerted within 1 h. After PV-M7 acted on Vibrio parahaemolyticus， it could increase the permeability of the cell membrane， leak the macromolecular substances (nucleic acid， protein) in the cell， at the same time， the surface of the cell membrane was blurred， and the density of the cytoplasm decreased. When PV-M7 contacts the cell membrane， its secondary structure changed from random coil to α-helical， this structural transformation was the key mechanism of its antibacterial activity.