The invention discloses a three-in-one liquid shampoo and a preparation method thereof. The three-in-one liquid shampoo is prepared from the following raw materials: sodium laureth sulfate, ammonium lauryl sulfate, behentrimonium chloride, cocamidopropyl MEA, cetanol, guar hydroxypropyltrimonium chloride, polyquaternium-10, allantoin, trimethylol propane octanoate ester, methylparaben, propyl hydroxybenzoate, C12-20 alkyl polyglycoside, cocamidopropyl betaine, cocamidopropyl dimethylamine oxide, dimethiconol or dodecylbenzene sulfonic acid TEA salt, zinc pyrithione, hydrolyzed keratin, hydrolyzed silk protein, methyl-isothiazol-ketamine, polyquaternium-7, essence, crylic acid (ester)/C10-30 alkanol acrylic ester cross-linked polymer and deionized water. By adopting the three-in-one liquid shampoo, the stability of the product and the use effects of the raw materials can be improved, the three-in-one liquid shampoo achieves good cleaning and nursing effects, does not generate aggregation and stimulation problems after being used for a long period of time, and achieves the three-in-one effect of cleaning, nursing and conditioning.