Hypochlorite (ClO^-), as an effective component of disinfectant and bleach, is commonly used in human production and life.The use of disinfectant containing hypochlorite in a small confined space has certain safety risks. At the same time, ClO^-participates in a number of life activities of human body in the body. Excessive ClO^- in the body will cause great harm to the immune system of human body and induce a variety of diseases.Therefore, it is necessary to detect ClO^- .In this paper, a cadmium sulfide quantum dot fluorescent probe was synthesized by one-pot method using polyethylenimine as the ligand to detect ClO^-. The results show that the probe has high selectivity and anti-interference ability in ClO^- recognition, and the detection range is 0~40 nmol/L, and the detection limit is 0.5 nmol/L.