The SL/T 788.1-2019 standard specifies a method for the determination of total nitrogen in water by continuous flow analyzer, which is suitable for the detection of total nitrogen in surface water, groundwater, drinking water, domestic sewage and industrial wastewater. The detection limit of this method is 0.016 mg/L (N) when the detection optical path is 50mm, and the measurement range is 0.065 to 5.00 mg/L. For samples beyond this range, it can be determined by appropriate dilution. The principle of the method is that the sample is digested under the action of excess potassium persulfate to form nitrate, the nitrate is then reduced to nitrite, the nitrite reacts with diaminobenzenesulfonic acid to form diazo compounds, and then reacts with α-naphthyl vinylenediamine to form advanced azo compounds. The total nitrogen concentration is quantitatively analyzed by measuring its signal value at 540/550 nm. The standard provides an accurate method for the determination of total nitrogen in water quality, ensuring the accuracy of water quality monitoring.