The invention relates to a preparation method of hydroxylamine hydrochloride, which comprises the following steps: dissolving diacetylmonoxime in hydrochloric acid, dissolving by heating and stirring, and stratifying by standing, wherein the supernatant is butanone, and the understratum is hydroxylamine hydrochloride; and adding activated carbon for decolorization, filtering, pouring the filtrate in ethanol, precipitating the crystal, filtering out the crystal, and drying to obtain the hydroxylamine hydrochloride. The synthesis method using water-soluble sodium salt is universal, easy to implement and simple to operate, and has the advantages of accessible raw materials and short period.