Abstract: The determination of NO 3 - concentration in H 2C 2O 4 stripping solution in TRPO process is studied. In H 2SO 4 solution, Fe 2+ reacts with NO 3 - and NO is liberated quantitatively. NO reacts with excess Fe 2+ immediately to form a colored nitrosyl complex which can be determined using spectrophtometric method. In the presence of sulfamic acid, determination of NO 3 - concentration is not affected with R (NO 2 -/NO 3 -) =3 and R (C 2O 4 2- /NO 3 -)=190. The minimum detection limit of NO 3 - concentration is 0.1 mg/L, the relative standard deviation of the method is 3%, the recovery of added standard sample is 97%～103%.