The development of high temperature proton exchange membranes (HT-PEMs) with high proton conduction and excellent mechanical properties remains a challenge. Herein, the graphitic carbon nitride (CN) nanosheets were successfully introduced into poly(ether sulfones)-poly(vinyl pyrrolidone) polymer matrix to prepare composite membrane through a facile blending method. The synthesized CN nanosheets were characterized by scanning electron microscope (SEM), Transmission electron microscopy (TEM), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). The proton conductivity of the composite membrane was improved up to 36% (0.104 S cm(-1)) after incorporating CN nanosheets at 160 degrees C, due to increased PA doping level and faster proton dissociation. Meanwhile, the tensile strength of the composite membrane is increased of 60% (6.0 MPa) compared to that of pristine membrane, because of the physical reinforced effect from the 2D structure of CN. Furthermore, the single cell fabricated with the optimized membrane exhibits a peak power density of 512 mW cm(-2) at the temperature of 160 degrees C for 200 h with no obvious loss of current density.