The invention discloses a signal demodulation method and a signal demodulation device used in an optical fiber distributed sensor system. The method comprises the following steps: obtaining a light pulse coding sequence and a signal after convolution of the light pulse coding sequence and the impulse response of an optical fiber to be detected; transforming the obtained light pulse coding sequence and the signal after convolution to a frequency domain through Fourier transform, and calculating the impulse response of the optical fiber to be detected in the frequency domain according to the transformed light pulse coding sequence and the transformed signal after convolution; and transforming the obtained impulse response of the optical fiber to be detected in the frequency domain to a time domain through Fourier inverse transform to get the impulse response of the optical fiber. According to the signal demodulation method and the signal demodulation device used in an optical fiber distributed sensor system of the invention, primary pulse input is adopted, and there is no need to consider whether the sum of complementary gray code autocorrelation is impulse response, so demodulation error is reduced.