Graphitic carbon nitride (g-C3N4) with improved photocatalysis was prepared via thermal polymerization of dicyandiamide with the assistance of calcium chloride. The photocatalytic activity of the modified product was optimized by changing the weight ratio of calcium chloride to dicyanodiamine, and the final products were characterized by XRD, FTIR, SEM, TEM, XPS, BET, DRS and PL spectra. The results indicate that calcium chloride could lower the crystalline sizes of g-C3N4 due to its coordination effect with the edge ammonia of g-C3N4. The Valence band level decreased after the modification with higher oxidation capability. The photo-generated hole and the superoxide radical are the main active species in the degradation process. As a typical performance, the degradation rate of the modified sample is more than 50 times higher than that of the un-modified carbon nitride. Due to the weakened visible light absorption of the modified catalyst, the degradation of RhB can be mainly attributed to its excitation and enhanced transfer of electrons to the catalyst. [GRAPHICS] .