Optical transmission delay could induce significant wavelength demodulation error to the fiber Bragg grating (FBG) interrogators based on tunable laser,especially when they are applied for remote and high-speed measurement of FBG sensors.A method for compensating the wavelength demodulation error of FBG induced by optical transmission delay is proposed.The optical frequency of tunable laser scans in up and down two directions with high linearity in its spectrum range.The wavelength demodulation error is compensated by the detected FBG reflection peak difference between up and down-scan spectrums.Experimental results show that,the wavelength demodulation error induced by optical transmission delay can be reduced from 2 nm to less than 10 pm after compensation,with measurement frequency of 50 kHz and optical fiber length of 100 m.