The invention discloses a plant disease-resistant fertilizer and a preparation method thereof. Main raw materials include mashed garlic, potassium carbonate, poplar tree root, potassium fulvate, carbendazol, waste tea leaves, sophora flavescens, bean dregs, a microbial strain agent, ageratina adenophora, ammonium nitrate, calcium superphosphate, potassium carbonate, ammonium nitrate, boric acid, sodium humate, cetyl alcohol, propylene glycol alginate, sodium selenite, urea phosphate, marble powder and tap water. Compared with a traditional formula, the invention has the following advantages: the materials of the formula are environmentally friendly, a few artificial chemical synthetic materials are adopted, and the influence on the environment is avoided; meanwhile, the soil fertility can be enhanced while the soil composition can be improved, the morbidity of anthracnose, vegetable leukoderma, sclerotinia rot of colza, cowpea sooty blotch, spot disease, wilt, damping off and verticillium wilt of crops is reduced, the yield of grain crops is increased, the rural income is raised, and the production cost of farmers is lowered; and therefore, the invention is particularly suitable for wide promotion and application.