This standard details the method for the determination of nitrate nitrogen in water using Ultraviolet spectrophotometry. Suitable for clean surface water and groundwater that is not significantly contaminated, the detection range is 0.08mg/L to 4 mg/L nitrate nitrogen. Water samples are treated using flocculation co-settling and macroporous neutral adsorption Resin under disturbing conditions such as dissolved organic matter, surfactants, etc. The principle of the method is to quantitatively determine nitrate nitrogen using the absorption of nitrate ions at a wavelength of 220nm, corrected by another measurement at 275 nm. The required instruments include an ultraviolet spectrophotometer, an ion exchange column, and commonly used experimental equipment.