GB/T 11897-1989 is a water quality testing standard. The N, N-diethyl-1,4-phenylenediamine Titrimetric method is used to determine free chlorine and total chlorine. Chlorine plays a key role in water quality treatment and disinfection, and its content is related to water quality safety. The standard specifies that after water samples are collected, the free chlorine and total chlorine content are determined by titration through reaction with reagents, and the steps of reagent preparation, titration operation and result calculation are specified in detail. The method is simple to operate and accurate. It is suitable for all kinds of water bodies. It provides key detection methods for water quality monitoring and water supply disinfection control, and ensures water safety and mass.