We proposed an system of optical time domain reflectometer with double repetition rates 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. What’s more, the measuring time was reduced. By adjusting the difference of the repetition rates, not only the mearsuring range of the system could be extended ,but also the measurement accuracy could be changed.