Due to their excellent carrier mobility,high absorption coefficient and narrow bandgap,most 2D IVA metal chalco-genide semiconductors (GIVMCs,metal =Ge,Sn,Pb;chalcogen =S,Se) are regarded as promising candidates for re-alizing high-performance photodetectors.We synthesized high-quality two-dimensional (2D) tin sulfide (SnS) nanosheets using the physical vapor deposition (PVD) method and fabricated a 2D SnS visible-light photodetector.The photodetector exhibits a high photoresponsivity of 161 A.W-1 and possesses an external quantum efficiency of 4.45 × 104％,as well as a detectivity of 1.15 × 109 Jones under 450 nm blue light illumination.Moreover,under poor illumination at optical densities down to 2 mW.cm-2,the responsivity of the device is higher than that at stronger optical densities.We suggest that a photo-gating effect in the 2D SnS photodetector is mainly responsible for its low-light responsivity.Defects and impurities in 2D SnS can trap carriers and form localized electric fields,which can delay the recombination process of electron-hole pairs,prolong carrier lifetimes,and thus improve the low-light responsivity.This work provides design strategies for detecting low levels of light using photodetectors made of 2D materials.