Graphitic carbon nitride nanosheet(Tg-3N4) was prepared by calcination and acid stripping using melamine as precursor. The structure and optical properties of Tg-C3N4were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), Fourier transform infrared spectrometry (FT-IR), N2 adsorption-desorption analysis,UV-vis absorption spectrometry (UV-vis) and photoluminescence spectrometry (PL). The visible light photocatalytic property of Tg-C3N4 was evaluated with methylene blue as the target pollutant. The results indicate that the thickness of Tg-C3N4 is about 1.0 nm,and the specific surface area increases from 6.04 m2·g-1 of g-C3N4 to 88.18 m2·g-1 of Tg-C3N4, which is about 14.6 times of that of g-C3N4. The fluorescence intensity of Tg-C3N4 is about 3/4 of that of g-C3N4. The recombination rate of surface photogenerated electron and hole pairs decreases. The photocatalytic efficiency of Tg-C3N4 can reach 90%, which is 57% higher than that of g-C3N4.