To improve the measurement range and reliability of fiber Bragg grating sensors,apodized ultra-short fiber grating was fabricated by single slit diffraction,its grating length is less than 1.5 mm,3 dB bandwidth is over 1.2 nm,and the edge linear region of the reflection spectrum is over 0.6 nm. Taking apodized ultra-short fiber grating as sensor unit,a central wavelength demodulation method based on linear region of the reflection spectrum is proposed. In order to make full use of the linear region on the two sides of reflection spectrum,the complementary demodulation method with dual-wavelength lasers is used to extend the wavelength demodulation range. The experimental results show that the linearity between optical power and the central wavelength is 0.992,and the dynamic demodulation range of the central wavelength is 2.4 nm. The measured values are in great agreement with the actual values. The method has the potential advantages of simple structure,low power consumption and high spatial resolution.