The invention discloses a preparation method of a foliar fertilizer with a lasting fertilizer effect, and belongs to the technical field of fertilizer preparation. The method comprises the following steps: processing mao bamboo to form powder, mixing and fermenting the powder with cellulase, pyrolyzing the obtained fermentation product, collecting a steam liquid, condensing the steam liquid, allowing obtained a crude pyroligneous liquor to stand for layering, sucking a middle layer liquid, mixing the middle layer liquid with active carbon, centrifuging the obtained mixture, stirring obtained supernatant and potato starch to form a viscous liquid, stirring and fermenting honey, soybean meal and urea, and stirring and mixing obtained fermentation liquid, the viscous liquid and a corn juice to obtain the foliar fertilizer. The foliar fertilizer prepared in the invention has the advantages of easily available raw materials, good green and nontoxic property, high utilization rate, less fertilizer loss, small affection of the lasting fertilizer effect by weather, no pollution to agricultural products or surrounding environment, and good economic prospect and social benefit.