The invention relates to a fresh keeping method of cucumis sativus. The fresh keeping method comprises the following steps of S1, adding milk derived antibacterial peptide to a chitosan acetic acid solution, and performing uniform mixing so as to obtain composite fresh keeping liquid, wherein the volume mass ratio of the milk derived antibacterial peptide to chitosan is (20-25) to 1mL/g; S2: sprinkling the composite fresh keeping liquid to the surfaces of the cucumis sativus, and performing airing; and S3, coating the surface of the cucumis sativus with a layer of fresh keeping films, and performing preservation. The fresh keeping method provided by the invention is good in fresh keeping effects of the cucumis sativus, the shelf life of the cucumis sativus can be effectively prolonged, loss of components of vitamin C, titratable acid, chlorophyll content and the like can be delayed, hardness of fruits is maintained, the commodity value of the fruits is maintained, and the fresh keepingmethod is environmentally-friendly, safe and good in application prospects.