Abstract: In order to study the dynamic response of structure subjected to the detonation of explosive charges, a direction sensitive optical-fiber displacement interferometer with the reference light modulated was made up of single-mode fiber elements, acousto-optic modulator and high-bandwidth amplified photodetector based on the laser Doppler effect and the heterodyne technique. The system had the advantages of compact, high dynamic response and non-contact measurement. The code for analyzing the raw data was compiled using the STFT algorithm. The viability of this system was demonstrated by measuring the velocity of a free surface of Hopkinson bar. The maximum velocity was 36.82 m/s and the velocity waveform was compared with results performed from strain gauge and calculated based on stress wave theory. The bidirectional velocity history of surface vibration obtained on the steel cylinder explosive experiment shows the system's ability of distinguishing the motion direction.