GB/T 11898-1989 is a water quality testing standard. The N, N-diethyl-1,4-phenylenediamine Spectrophotometric method, spectrophotometry is used to determine free chlorine and total chlorine. Chlorine is commonly used in water treatment, and its content is related to the disinfection effect and safety of water quality. The standard specifies the operation from the collection of water samples, the addition of reagents and the reaction of chlorine color, to the calculation of free chlorine and total chlorine content by spectrophotometer measurement Absorbance. This method is standardized and reliable, and is suitable for all kinds of water bodies. It provides key detection means for water quality monitoring and water supply system disinfection control to ensure water safety.