The invention provides a preparation method of a vegetable freshness-keeping agent. The preparation method of the vegetable freshness-keeping agent comprises the following steps: a, performing processing treatment on a chitosan solution, mixing the processed chitosan solution with sodium alginate, astaxanthin and sodium citrate, and carrying out stirring while heating so as to obtain a material one; b, mixing a radix isatidis extract and a pomegranate peel extract with soybean protein, and carrying out heating and stirring so as to obtain a material two; c, performing pretreatment on fresh ginger, adding an organic solvent, carrying out heating, carrying out filtration, and carrying out steaming until the mixture is dried so as to obtain an extract; and d, uniformly mixing the material oneand the material two with the extract, adding a beeswax-oil mixture, and carrying out heated dispersing treatment so as to obtain the vegetable freshness-keeping agent. The vegetable freshness-keeping agent prepared by the preparation method has the characteristics of good stability, simple manufacture process, non-pollution to the environment, and long preservation time.