The invention discloses a synergist for improving the gram-positive-bacterium-resistant effect of nisin. Microdilution method drug susceptibility tests and chessboard type microdilution tests are used, tested bacteria comprise nine staphylococcus aureus food isolated strains, nine listeria monocytogenes food isolated strains and two quality-control strains for contrast, that is, staphylococcus aureus ATCC 29213 and listeria monocytogenes ATCC 19115, the effect caused by perilla oil on the antibacterial activity of the nisin is measured, and test results prove that the perilla oil has the effect of enhancing the gram-positive-bacterium-resistant activity of the nisin. The nisin is a polypeptide antibiotic substance extracted from a streptococcus lactis fermentation product, can be degraded by some proteases in human body digestive tracts easily, and has no adverse effect on colors, aromas, tastes and the like of food, and perilla is rich in alpha-linolenic acid and has effects of resisting oxidation, resisting ageing, resisting thrombus, preventing and treating cardiovascular diseases, resisting cancers, resisting allergies and resisting inflammations. High-nisin and the perilla oil are used as food preservatives, the additive amount of the high-nisin can be decreased, safe and reliable purposes can be achieved, and the health-care effect can be realized.