The invention provides a preparation method for a foliar fertilizer. The foliar fertilizer is prepared by mixing biochemical fulvic acid powder, ammonium sulfate, dipotassium hydrogen phosphate, potassium nitrate, threonine, leucine and water in proportion and then carrying out a stirring reaction. The prepared foliar fertilizer can provide a plurality of nutrient elements needed by crops, improves activity of trace elements, reduces the usage amount of pesticides, lowers cost, enhances drought resistance and cold resistance of crops, promotes growth of crops and improves the utilization rate of photosynthesis.