GB/T 13905-1992 is a water quality testing standard, using sodium sulfite Spectrophotometric method, spectrophotometry to determine TNT (TNT). TNT, as a common explosive component, may enter the water body with industrial wastewater, endangering the environment and health. The standard details the process of water sample collection, pretreatment and sodium sulfite reaction color, and then spectrophotometer Absorbance to determine TNT content. There are clear specifications from reagent preparation, operation steps to result calculation. Sensitivity and accuracy of this method are high, suitable for all kinds of water samples contaminated by TNT, providing key technical support for water quality monitoring, pollution prevention and control, and safeguarding water environment safety.