Based on the principle of tunable fiber Fabry-Perot(TF F-P) filter which scans the reflected peak of fiber Bragg grating(FBG),a novel detection method is advanced.The synthesis of reflected and transmitted spectrum is monitored in dynamic and static state respectively,which is realized by the different signals driving TF F-P filter.The chart between light power and voltage is simulated and analysed in the static state,and the dynamic signal is detected with the oscillograph.The experimental result is consistent with the theoretic analysis.Wavelength resolution of 1 pm and measuring precision of 0.01 nm are obtained in the calibrated system.