The SL/T 788.4-2019 standard specifies a method for the determination of anion surfactants in water using a continuous flow analyzer. The method is suitable for the detection of anion surfactants in surface water, groundwater, drinking water, domestic sewage and industrial wastewater. When the detection optical path is 50mm, the detection limit of the method is 0.010 mg/L, and the determination range is 0.040~ 1.00 mg/L; for samples with concentrations higher than this range, an appropriate diluted post-determination can be carried out. Anion surfactants, such as sodium dodecylbenzene sulfonate (LAS), are mixtures of multiple ingredients and are commonly found in detergents. The standard provides a method for the accurate determination of anion surfactants in water to ensure the effectiveness and accuracy of water quality monitoring.