The discharge of dye wastewater has become a serious threat to human health and the ecosystem. Photocatalytic technology has shown attractive potential in eliminating environmental pollution problems owing to its simple operation and environment-friendly. Graphite-like phase carbon nitride (g-C₃N₄) was considered to be one of the most promising photocatalysts for its low cost and high chemical stability in the field of photocatalysis. However, poor specific surface area, limited optical absorption and high charge carrier recombination rate restricted its photocatalytic efficiency. Thus, a novel graphitic carbon nitride(g-C₃N₄-N) photocatalyst was synthesized by thermos-induced copolymerization modification method using urea and o-Aminobenzontrile, and its effect on photocatalytic degradation ability of RhB was evaluated based on solution pH value, g-C₃N₄-N dosage, and RhB concentration. In addition, both the photocatalytic degradation mechanism of RhB and its degradation path by g-C₃N₄-N were also analyzed through XRD, BET, UV-Vis in this research. The results showed that g-C₃N₄-N synthesized using copolymerization modification method was pure graphite-like phase g-C₃N₄-N, with the stable performance of a photocatalytic activity, large specific surface area and porous structure. Under visible light conditions, the photocatalytic degradation efficiency of RhB was found to be optimal with initial pH of 3, RhB concentration of 10 mg·L^-1 and g-C₃N₄-N dosage of 50 mg, and the adsorption removal rate of RhB was achieved 30% within 30 minutes in dark reaction. Besides, its photocatalytic degradation removal rate of 120 minutes reach 97.7%. Under the catalysis of visible light, RhB molecules adsorbed on the surface of the g-C₃N₄-N was firstly degraded into macromolecular intermediates such as DER, EER and AR through rapid N-de-ethylation process, then base on redox reaction of holes, ·OH and ·O2-, conjugated structure of these intermediates was cracked and ring-opened to generate some small molecules, such as succinic acid, resorcinol, and propionic acid, and so on. After that, the removed ethyl groups were gradually oxidized to ethylene glycol. And these small molecules were eventually mineralized into CO₂ and H₂O.