Denitrification of ammonia and nitrate through SCWO has been investigated under a stable pressure of 24 MPa, temperature and reaction time of 350-550 degrees C and 0.5-6 min, respectively. The result showed that an appropriate ratio of NO3- /NH4+ did facilitate TN removal, which resulted in the best ratio of 1:1. The reaction of NO2-/ NH4+ achieved a better TN removal than that of NO3-/NH4+. The catalysts, like Co2+, Zn2+, Cu2+ and Fe3+, and co-fuels, such as methanol, ethanol and isopropyl alcohol, could play a positive role on TN removal. The results indicated that the highest degradation rate constant was found in the presence of isopropyl alcohol (IPA). The distribution of NO3- and NH4+ showed that the concentration of nitrate was much higher than that of ammonium, which revealed that the conversion of ammonia made a major contribution to TN removal.