Abstract: Porous graphite phase carbon nitride (PCN) was prepared by modifing graphite phase carbon nitride (g-C₃N₄) via thermal polymerization with melamine as raw material, and calcium carbonate as auxiliary template. The adsorption characteristics and effects of U(Ⅵ) by modified g-C₃N₄ before and after modification were studied. Characterization methods such as SEM, BET, FT-IR and XPS were used to analyze the adsorption mechanism of the PCN for U(Ⅵ). The results show that the specific surface area (58.5 m²/g) of PCN increases significantly, which is about 4 times of that of g-C₃N₄. The maximum adsorption capacity of PCN for U(Ⅵ) is 92 mg/g at the proper conditions of pH=5, the adsorption time of 2 h, the initial U(Ⅵ) concentration of 10 mg/L, the dosage of adsorbent of 0.2 g/L and the temperature of 303 K. The adsorption is well fitted to the second order kinetic equation and the Langmuir isothermal adsorption model, FT-IR and XPS confirm that the nitrogenous group on PCN is involved in the adsorption of U(Ⅵ).