The invention provides an oral antibacterial composition containing nisin and polylysine. According to the composition, the growth of oral pathogenic bacteria such as porphyromonas gingivalis, actinobacillus actinomycetemcomitans, streptococcus mutans, lactic acid bacillus, staphylococcus aureus and candida albicans can be effectively inhibited, and tooth decay, gingivitis, periodontitis, ozostomia and the like can be prevented; the composition can be prepared into toothpaste, mouth wash, refreshing and tasting chips and chewing gum which are used for preventing and treating oral diseases. Meanwhile, the invention provides a preparation method of the compositions such as the toothpaste, the mouth wash, the refreshing and tasting chips and the chewing gum. The oral antibacterial composition prepared through the method can prevent and treat various oral diseases and has no toxic and side effect and allergy or stimulation phenomenon on a human body.