The invention provides a preparation method for a foliar fertilizer. The foliar fertilizer is prepared by mixing biochemical fulvic acid powder, urea, potassium dihydrogen phosphate, potassium sulfate, citric acid, methylenesuccinic acid and water in proportion and then carrying out a stirring reaction. The prepared foliar fertilizer can effectively increase yield of crops, improves disease resistance and stress resistance of crops and prevents the problems of disproportionality of nutritive elements and changes of the trophic structure of soil due to long-term usage of compound fertilizer only containing macroelements.