Abstract: In the distributed fiber-optic disturbance sensor system based-on -OTDR, the frequency drift of laser directly results in low signal to noise ratio(SNR) of the system and further influences system location. In order to reduce the disturbance location error induced by laser frequency drift, a location algorithm was proposed through analyzing the error mechanics, which combines spectrum analysis with characteristic frequency selection. The characteristic frequency for location was achieved by comparing the SNR of the system owing to different frequency. Laboratory tests were established and the results indicate that the algorithm is efficient to disturbance location for the location and the performance of system has been enhanced.