The invention discloses a fulvic acid water-soluble foliar fertilizer and a preparation method thereof. The fulvic acid water-soluble foliar fertilizer comprises the following active ingredients in parts by weight: 30-40 parts of sodium fulvate, 40-50 parts of potassium dihydrogen phosphate, 20-30 parts of urea, 10-15 parts of ammonium sulfate, 25-35 parts of waste silk, 15-20 parts of feather meal, 5-10 parts of monosodium glutamate leftovers, 2-3 parts of zinc nitrate, 1-2 parts of manganese sulfate, 1-2 parts of magnesium sulphate, 0.5-1.5 parts of sodium molybrate, 1-2 parts of boric acid, 0.5-1 part of thylenediaminetetraacetic acid disodium, 10-15 parts of kelp residues, 5-10 parts of rape seed cakes, 8-12 parts of soyabean meal, 5-10 parts of brewer's grain, 8-12 parts of waste methane liquid, 2-3 parts of luffa stem, 1.5-2.5 parts of cortex meliae, 1-2 parts of tung tree roots, 2-3 parts of radix sophorae flavescentis, 1-2 parts of thunder god vine, and 2-3 parts of castor plant leaves. The foliar fertilizer is complete and balanced in nutrients, high in fertilizer efficiency, high in fertilizer utilization rate, capable of fast replenishing the nutrition for crops, also has the effects of disease prevention, antibiosis, insect killing, insect expelling, flower retention, fruit retention and the like, is obvious in effects of reducing the plant disease and insect pest of crops, reducing the use of chemical pesticide, promoting fast growth of crops, enhancing the stress tolerance of crops, improving the quality of crops and increasing both production and income, and has tremendous economic benefits.