A demodulation scheme based on Polarizing Beam Splitters (PBS) and inter-modal polarization interference in Polarization-maintaining Fibers(PMFs)was proposed to implement the wavelength demodulation of fiber Bragg grating sensors and to improve their precisions and stabilities. Using the principle of matrix optics, the mathematic model was established theoretically and the relations of system output signals and Bragg wavelengths of fiber gratings were obtained. The influences of the length of the polarization-maintaining fiber,polarized angles of input light to the principal axis of PMF and the orientation of PBS principal axis on output signals were researched and a method to improve the sensitivity of the system was presented. On the scheme above,an experimental system was set up. The results demonstrate that the scheme is feasible, in which the average precision of the wavelength demodulation is lower than 1 pm and the temperature measurement range is 90 ℃. The demodulation system has higher precision and its stability is better than that of the M-Z interference device.