An optical time domain reflectometer with dual repetition rates was proposed based on the single photon detector with InGaAs/InP avalanche photodiode. Two arrays of laser pulses with slight different repetition rates were injected into the fiber to monitor the fiber broken point. A fast single photon detector was adopted for high sensitivity in reflected pulses detection with reduced measurement time. By adjusting the difference of the repetition rates, not only the measuring range of the system can be extended ,but also the measurement accuracy can be changed.