In order to measure the signals greater than kHz such as vibration, high frequency strain and ultrasonic wave, a high-speed demodulation system for fiber Bragg grating（FBG）sensor based on tunable laser light was established. The measuring principle of the demodulation system was presented. The output curve and the wavelength measurement sensitivity were given by theoretical deduction. Then the 41434.71028 [Hz] vibration signal of ultrasonic cleaner was measured using this system. The system was compactly built with high demodulation speed and S/N(signal to noise ratio), meeting the special requirement for the high frequency signals measurement.