Based on the reaction that 2,3-diaminonaphthalene(DAN) has the ability trapping ^·NO to yield the highly fluorescent 2,3-naphthotriazole, a new fluorometric method has been reported, which combines the nitrogen gas purging system and fluorescent analysis together. The results indicated that the fluorescence intensity of the measuring solution is ^·NO concentration and acidified nitrite concentration dependent. Five acidified samples of normal human plasma have been determined and the released ^·NO is about (31.04±4.70) nmol/L. Since this method separates the sample from the measuring solution, it can avoid the interference from the sample to the fluorescence analysis so that it can be used to measure biological sample and continuously observe the ^·NO releasing.