The invention relates to a jerusalem artichoke blade phenolic extract, as well a preparation method and application of the jerusalem artichoke blade phenolic extract. The preparation method comprises the following steps of: drying fresh jerusalem artichoke blades, and crushing the fresh jerusalem artichoke blades to obtain dry powder of the jerusalem artichoke blades; putting the dry powder of the jerusalem artichoke blades into a decompression reflux extraction device, adding de-ionized water, extracting at room temperature to obtain a water phenolic extract, and concentrating or drying the water phenolic extract; or, adding an organic solvent into the decompression reflux extraction device, extracting while refluxing or decompressing and refluxing, and concentrating or drying to obtain an organic solvent phenolic extract; and extracting the water phenolic extract of the jerusalem artichoke blades or the organic solvent phenolic extract by using petroleum ether, chloroform, ethyl acetate and n-butyl alcohol respectively in turn according to the volume ratio in a stepwise manner, and finally, concentrating and drying to obtain the stepwise phenolic extract. The extract disclosed by the invention belongs to the novel plant-source (vegetative) pesticide, has specially good effects on a plurality of plant pathogenic bacteria, such as botrytis cinerea, phytophthora capsici leonian, colletotrichum gloeosporioides, rhizoctonia cerealis and gaeumannomyces graminis, and also can be used as a natural plant-source fungicide and a preservation preservative of fruits and vegetables.