In order to gain the wavelength of fiber Bragg grating sensor system precisely，by analyzing the shortcoming of traditional methods，an improved threshold selection strategy is proposed，and a new threshold function is built to deal with FBG signal.The reasonable selection of wavelet basis and decomposition scale can improve the performance of de-noising.A method is put forward about wavelet basis and decomposition scale.The result of simulation and experiment show that the signal noise ratio(SNR)can increase by 2dB to 4dB compared with the traditional soft threshold and hard threshold method.While compared with the reference method，the SNR improves 1.5dB.This method can meet the need of precise demodulation FBG wavelength.