A wavelength demodulated method of fiber Bragg grating (FBG) is proposed to measuring pulse signal, which can be applied to smart clothing. Based on the photonic crystal fiber (PCF), a kind of Mach- Zehnder interferometer (In-line MZI) is fabricated on the basis of mode interference. The interferometer works as an edge filter in the wavelength demodulation system of FBG. The temperature sensitivity of the interferometer is lower than 3.5 pm/℃ (range from 25 ℃ to 60 ℃ ). The experiment results indicate that the system can achieve linear demodulation within the range of 2 nm, with a wavelength sensitivity of 0.055 nm^-1 and a wavelength resolution of 2.2 pm. The demodulation results of FBG pulse signal measured from the proposed system are consistent with the results measured from SM130 demodulation instrument.crystal fiber