A novel photon-counting optical time-domain reflectometry (ν-OTDR) based on superconducting nanowire single-photon detector (SNSPD) is proposed and demonstrated experimentally. Benefiting from the low noise equivalent power (NEP), high repetition rate and low timing jitter of the SNSPD, our ν-OTDR system achieves a dynamic range of 22 dB after measurement time of 15 minutes. This obtainable dynamic range corresponds to a sensing length of 110 km. The system exhibits 6.0 cm spatial resolution at the end of 2 km and 1.1 m spatial resolution at the end of 26 km standard single-mode fiber. Considering the performance we obtained now and the increasing improvement of the fabrication technology, the SNSPD is promising in the field of fiber sensors.