A tobacco foliar fertilizer and a preparation method thereof. The tobacco foliar fertilizer includes following components, by weight: 20-25 parts of potassium tripolyphosphate, 15-20 parts of potassium citrate, 3-6 parts of sargassum fermentation extract, 0.5-2 parts of glutathione, 0.5-2 parts of [beta]-deoxyglucose, 0.1-1 part of trans-abscisic acid, 0.5-1 part of xylooligosaccharide, 0.2-0.5 parts of salicylic acid, 1-3 parts of boric acid, 0.1-0.5 parts of ammonium molybdenate, 0.5-2 parts of EDTA-chelating zinc, 0.5-2 parts of EDTA-chelating magnesium, 0.3-2 parts of EDTA-chelating manganese, 0.3-1 part of EDTA-chelating copper, 0.5-1 part of alkyl polysaccharide glycoside and 31-56.2 parts of water. The tobacco foliar fertilizer is reasonable in combination and proportion, can promote growth of tobacco, can enhance the resistance capability on viruses, cold and dryness of tobacco, can increase yield, is green and environmental-friendly and can greatly improve quality of tobacco.