The invention relates to a skin antibacterial agent and a preparation method thereof. The skin antibacterial agent comprises components such as ginkgo leaf juice, white chrysanthemum juice, eggplant root juice, kudzuvine root juice, mugwort leaf juice, portulaca oleracea juice, fistular onion stalk juice, distilled water and the like. The preparation method for the skin antibacterial agent comprises the following steps of: mixing the ginkgo leaf juice, the white chrysanthemum juice, the eggplant root juice, the kudzuvine root juice, the mugwort leaf juice, the portulaca oleracea juice, the fistular onion stalk juice and the distilled water, stirring uniformly, heating for 6 to 8 hours at the temperature of 65 to 70 DEG C, adding an auxiliary raw material into the mixed solution to ensure that the mixed solution is subjected to catalytic reaction, and thus obtaining the skin antibacterial agent, wherein a biological monitor in a catalytic reaction device is used for automatically tracking and testing in the process of the catalytic reaction. The invention has the advantages that: the skin antibacterial agent has wide sterilization spectrum, is low in effective concentration, quick in response and stable in performance, greatly improves healing degree of wounds and relieves pain of patients in the process of changing and applying medicines; and in addition, the preparation method for the skin antibacterial agent is simple and convenient to operate.