The preliminary purification and antimicrobial mechanism of antimicrobial peptide from Antarctic Krill were studied in this paper.The results showed that the molecular weight range of antimicrobial polypeptide(CMCC-1) obtained by cation exchange chromatography was between 245-709D as detected by molecular sieve chromatography,and the minimum inhibition concentration(MIC) of CMCC-1 against Staphylococcus aureus was 5.0 mg mL-1.The antimicrobial mechanism of CMCC-1 was studied with S.aureus as indicator bacterium.Compared with control group,the results of the experimental group in which S.aureus was treated with CMCC-1 were as follows: 1) CMCC-1 could inhibit cell division at logarithmic phase.2) The protein and reducing sugar content,and the conductivity of culture medium increased,and the activity of alkaline phosphatase and β-galactosidase could be detected in the culture medium.3) Observation under scanning electron microscope revealed that somatic morphology became irregular,and then somatic surface became coarse.The cell became much smaller,and most somatic cells gathered.The boundary between cells became dim and finally fused as a whole.4) Observation under transmission electron microscope showed that the surface of S.aureus became rough and the reproducing ability was restrained.The cell wall became thin and the cytoplasm shrunk.Substances inside cell leaked out,which caused cells death.5) SDS-PAGE analysis showed that some bands disappeared,and the residual bands became vague.6) The genomic DNA electrophoresis results showed that the genomic DNA bands of S.aureus were not degraded but the brightness significantly reduced.Thus,it is supposed that CMCC-1 could destroy the cell wall and membrane of S.aureu,increase the cell membrane permeability and the leaking-out of intracellular substances,and thus cause the death of S.aureu. The preliminary purification and antimicrobial mechanism of antimicrobial peptide from Antarctic Krill were studied in this paper showed the the weight weight range of antimicrobial polypeptide (CMCC-1) obtained by cation exchange chromatography between 245-709D as detected by molecular sieve chromatography , and the minimum inhibition concentration (MIC) of CMCC-1 against Staphylococcus aureus was 5.0 mg mL-1. The antimicrobial mechanism of CMCC-1 was studied with S. aureus as indicator bacterium. Compared with control group, the results of the experimental group in which S. aureus was treated with CMCC-1 were as follows: 1) CMCC-1 could inhibit cell division at logarithmic phase. 2) The protein and reducing sugar content, and the conductivity of culture medium increased, and the activity of alkaline phosphatase and β-galactosidase could be detected in the culture medium.3) Observation under scanning electron microscope revealed that somatic morphology became irregular, and th en somatic surface became coarse.The cell became much smaller, and most somatic cells gathered.The boundary between cells became dim and finally fused as a whole.4) Observation under transmission electron microscope microscope showed that the surface of S.aureus became rough and the reproducing ability was restrained.The cell wall became thin and the cytoplasm shrunk.Substances inside cell leaked out, which caused cells death.5) SDS-PAGE analysis showed that some bands disappeared, and the residual bands became vague.6) The genomic DNA electrophoresis results showed that the genomic DNA bands of S. aureus were not degraded but the brightness significantly reduced. It, it is supposed that CMCC-1 could destroy the cell wall and membrane of S. aureu, increase the cell membrane permeability and the leaking -out of intracellular substances, and thus cause the death of S. aureu.