Superconducting nanowire single photon detector (SNSPD) is an optical detector with quantum-limit sensitivity. The detection mechanism is based on the Cooper-pair breaking by the photon energy, which results in a phase transition from superconducting state to non-superconducting state. SNSPDs surpass the semiconducting counterparts with high detection efficiency, low dark count rate, small timing jitter, short dead time, broad spectrum sensitivity as well as free-running etc. SNSPDs with high performance have been applied in various fields, such as, quantum information, laser communication, light detection and ranging. The progress of SNSPD research and development, application as well as commercialization at home and abroad in the past few years was summarized. An outlook of SNSPDs′ R&D as well as applications was also provided.