Vibrio parahaemolyticus is a common foodborne pathogen that impacts food safety and public health. In this study， peptides were screened from Lacticaseibacillus paracasei fermented broth and identified by ultra-high performance liquid chromatography-mass spectrometry. One of the peptides， named Yt9z (RQQAENLAKFAKKG) with antibacterial potential was further screened by bioinformatics. The minimum bactericidal concentration (MBC) of Yt9z against V. parahaemolyticus was 125 μg/mL， with all the bacteria being killed within 3 h. The antibacterial mechanism of Yt9z was further explored through membrane permeability， transmission electron microscope， DNA gel， and circular dichroism. The results showed that peptide Yt9z could change its secondary structure in different environments， which increased the membrane permeability. Moreover， peptide Yt9z penetrated bacteria membranes to kill the bacteria by DNA binding. These findings provide a theoretical basis for the application of peptide Yt9z in the control of V. parahaemolyticus contamination.