Mid-infrared (mid-IR) single photon detectors have broad applications in science and technology, such as biomolecular spectrum analysis [1] and astronomical observations [2].Unfortunately, it is much more difficult than detecting near-infrared photons due to the significantly reduced energy of mid-IR single photon.Superconducting nanowire single photon detectors (SNSPDs) have shown a great potential in mid-IR single photon detection relied on the low energy gap (～meV) of superconductor materials.In 2011, Marsili et al.[3] extended the response bandwidth of SNSPD to 0.5-5 μm band by reducing the width of NbN nanowire to 30 nm, resulting in a saturated internal detection efficiency at wavelengths λ ＜ 3 μm.The reduced width of 30 nm increased the probability of the transition from the superconducting state to the non-superconducting state.In 2019, Verma et al.[4] reported a SNSPD based on WSi films, a superconductor material with low energy gap, achiving a response cut-off wavelength at 9.9 μm.The lower energy gap of WSi enhanced the efficiency of the photon-induced Cooper pair decoupling.As can be seen above,it is an effective way to develop mid-IR SNSPD through ultranarrow nanowires patterned on superconductor films with low energy gap.