Polyvinylpyrrolidone (PVP) owned the apparent fluorescence characteristics. In the presence of a small number of Fe3+, the interaction between Fe3+ and PVP could lead to an obvious decreasing of PVP fluorescence. However, when a small amount of F-was added in Fe3+-PVP system, the fluorescence intensity could partly been restored, which was ascribe to the formation of [FeF6]3- complexes. Thus, a new Off/On fluorescence spectrophotometry was established for the detection of fluoride. Under the optimized experimental conditions, the fluorescence recovery degree showed a good linear relationship with the fluorine ion concentration in the range of 1.5-30.0 μmol/L. A detection limit as low as 0.6 μmol/L was obtained. This method was applied to the detection of fluoride ion in fish meat with satisfactory results. The recovery rates were between 93.33% and 100%.