An infrared detector with high responsivity based on graphene-PbSe thin film heterojunction was reported.High-quality PbSe thin film and graphene were prepared by molecular beam epitaxy and chemical vapor deposition,respectively.The physical characteristics of PbSe thin film and graphene were performed using X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and Raman measurement.The phototransistor using PbSe thin film as a sensitizer and graphene as a channel to transport excitons exhibits peak responsivity and detectivity up to~420 A·W-1 and 5.9×1011 Jones(radiation intensity:0.75 mW·cm-2)at room temperature in the near-infrared(NIR)region,respectively.The high optical response is attributed to the photo-excited holes transferring from PbSe film to graphene under irradiation.Moreover,it is revealed that the responsivity of graphene-PbSe phototransistor is gate-tunable which is important in photodetectors.