Abstract: A new fluorimetric method for determination of nitrite was studied, based on the reaction of 5-aminofluorescein in acidic medium to form a new compound which was no fluorescence and reduced to highly fluorescence in alkaline medium. Effects of metal ions impurity were discussed. The acidity and measuring time were given. The precision of this method are 4% and 5% respectively. The recoveries are between 96% and 106% in nuclear fuel reprocessing solution and between 96% and 103% in high-level radioactive liquid waste. The method is applied to the determination of NO^-₂ in nuclear fuel reprocessing solution and high-level radioactive liquid waste and nitrocompound in organic liquid waste.