Abstract: UV-irradiation has been known as an effective method for measuring the amount of total organic nitrogen of low concentration in natural water. In our work we have made some improvements: First, we have found that K₂S₂O₈ and H₂O₂ as a mixed oxidant is more effective than other oxidants so that the irradiating time may be shortened from 2-4 hours to only 20 minutes. Secondly, the procedure for adjusting the pHhas been simplified. The pHcan be maintained in basic solution without the two-step irradiation or the addition of buffers. Thirdly, the quantitative recoveries of the common pollutants in solution, such as aniline and nitrobenzene, can be obtained. In this paper we also discuss the interference problems during the irradiating process, the influences of the concentration and structure of organic nitrogen compounds in the photo-oxidation process. Finally, we discuss the use of this method to analgze samples taken from the Songhuajiang River.