The invention discloses long-acting hair-blacking liquid and a preparation method thereof. The hair blacking liquid is prepared from water, benzyl alcohol, butanediol, hydroxyethyl cellulose, arginine, a polyamino acid polysaccharide condensate, xanthan gum, bis (lauramide glutamine) lysine sodium, a radix polygoni multiflori extracting solution, an angelica sinensis SINNENSIS extracting solution, a chlorella extract, a gallnut extracting solution, ethanolamine, vitamin B5, ammonia-terminated polydimethylsiloxane, sodium pyrrolidone carboxylate, sodium lactate and dipotassium glycyrrhizinate. The hair blacking liquid is prepared from schizophyllan, glycine, pyrrolidone carboxylic acid, serine, isoleucine, threonine, CI20470, PEG-40 hydrogenated castor oil, histidine, sodium benzoate, essence and EDTA (ethylene diamine tetraacetic acid) disodium, and the prepared hair blacking liquid is convenient to use, low in cost, small in dosage, quick in effect and long in effect time.