Abstract: In order to achieve a high accuracy measurement of the strain parameters of the spacecraft structure with optical fiber sensors, in the space environment of high and low temperatures, a demodulation approach with a composite wavelength reference is adopted, with the Fabry-Perot(F-P) etalon and the acetylene(C₂H₂) gas cell being used together to calibrate the transmission wavelength of the tunable filter. An adaptive threshold method is adopted to improve the peak finding process of the F-P etalon in spite of the flatness of the light source. Meanwhile, the light source signal passed through the gas cell is separated blindly based on the principle of the time prediction maximization, so as to improve the precision of the wavelength calibration for the gas cell. It is shown that the deviation of the wavelength demodulation with the above approach is less than 3 pm in the temperature scope of -25 ℃ to 60 ℃, and the relative measurement error of the structure strain is less than 4%. With this method, the requirement of the accurate measurement of the strain parameters for spacecraft structures can be satisfied in various engineering applications.