The invention relates to a plant wound protective agent containing chitosan oligosaccharide which contains chitosan oligosaccharide and one or more of a nutritional agent, an adjusting agent and a sterilizing agent, wherein the weight percentage of the chitosan oligosaccharide accounting for the protective agent is 0.0015-0.03 percent. The plant wound protective agent can be used for spraying or smearing. The prepared solid preparation for smearing also contains a film-forming agent. On one to five days before pruning, girdling or grafting, the wound is sprayed by using the protective agent; and on one to five days after the pruning, girdling or grafting, the wound is smeared by the protective agent, so that disease attacks of the wound can be reduced and the healing of the wound can be promoted. The plant wound protective agent is used for apple trees, pear trees, peach trees, jujube trees, grape trees, mango trees, longan trees, lychee trees, citrus trees, watermelon, maidenhair trees, honeysuckle, Arabian jasmine flower and Chinese rose.