Abstract In this experiment, a method for continuous detection of Fe 3+ and F - based on the fluorescence “OFF-ON” of quinine sulfate was designed. Through the addition of Fe 3+ , the fluorescence spectrum of quinine sulfate appeared “OFF”. Then, when F - was added, the fluorescence appeared “ON” again. By this method, we can get the quantitative detection of Fe 3+ and F - continuously. The detection limit of Fe 3+ is 1.0×10 -5 mol/L and the linear range is 4×10 -5 mol/L-8×10 -4 mol/L. The detection limit of F - is 4.4×10 -5 mol/L and the linear range is 1.2×10 -4 mol/L-2.4×10 -3 mol/L.