In the acidic medium, hydrosulfuryl(-SH) in cysteine hydrochloride can reduce Fe³⁺ to Fe²⁺, then Fe²⁺ react with potassium ferricyanide to form KFe[Fe(CN)₆](soluble Prussian blue). Prussian blue has a maximum absorption at 727 nm, Bill’s law is observed between mass concentration of cysteine hydrochloride and absorbance of Prussian blue, the content of cysteine hydrochloride is indirectly determinated by measuring the absorbance of Prussian blue. An accurate, simple, fast spectrophotometric method for the determination of cysteine hydrochloride content by ferric chloride-potassium ferricyanide has been established. The optimal determination conditions of cysteine hydrochloride content are explored. The cysteine hydrochloride content is determinate by this method.