Single-photon detectors have been widely used in many vital fields, such as quantum teleportation and quantum computation. Compared with other single-photon detectors, superconducting nanowire single-photon detector exhibits relatively wide response spectrum, low dark count rate and high detection efficiency. The principle of superconducting nanowire single-photon detector is demonstrated, especially on the process of the generation and the diffusion of the hotspot, and the simulation is done to illustrate this process. Many important parameters of superconducting nanowire single-photon detector are measured, such as R-T curve and photon response. Through the analysis of experimental data, the approach to improve the performance of superconducting nanowire single-photon detector is proposed.