The invention relates to a functional hair washing shampoo and its preparation method. The functional hair washing shampoo comprises the following substances, by weight, 10 parts of sodium dodecylpolyoxyethylene ether (2EO or 3EO) sulfate, 3.5 parts of ammonium dodecyl sulfate, 1.2-1.6 parts of cocounut oil/palm kernel oil fatty acid monoethanolamide/diethanolamide, 2.5 parts of an alkyl glucoside, 1.5 parts of cocoamidopropyl betaine, 3 parts of glycerin, 0.1 parts of disodium ethylene diamine tetraacetate, 0.5-0.7 parts of sodium chloride, 0.1-0.2 parts of an essence and 76.9-77.6 parts of deionized water. The functional hair washing shampoo has the advantages of no damage to hair and scalp, no excitation to skins, mucous membranes and eyes, no other adverse effects, good dry and wet combing properties, softness, moisture and shining of the hair after washing, no hardening, no flying, easy fixing, excellent foaming property, obvious decontamination effect, simple formal technology, low cost, high cost performance, and strong market competitiveness.