To satisfy the requirements of high-speed and high-precision demodulation applications,an adaptive semi-peak-seek algorithm based on state machine is proposed.The proposed algorithm determines the waveform data by real-time tracking of the FBG reflection waveform.Through statistical analysis of the waveform data,a peak-seek threshold can be achieved,and then the precise position of the peak can be obtained by means of calibration and compensation.From the experimental results,the demodulation distinguishability can reach 1 pm while the demodulation speed is 2 kHz,at the same time the static noise is less than ±2 pm.The stability error of less than 2 pm is concluded in a long term test.As the system dynamic range is from 0 to ~-30 dB,the measurement error within the dynamic range is limited to 4 pm.Thus,the requirements of high-speed demodulation,such as speed,precision,stability and anti-interference properties,can be achieved by this algorithm.