A TiO₂ trapped meso/macroporous g-C₃N₄ heterojunction (mm-CNT) photocatalyst is fabricated by hydrolysis and sintering of tetrabutyl titanate on meso/macroporous g-C₃N₄ prepared via a facile hard template method. TiO₂ nanoparticles are highly dispersed and some of them are trapped in the pores of meso/macroporous g-C₃N₄. The photocatalytic performance of mm-CNT is assessed through degradation of Rhodamine B solution under visible light irradiation, which displays much better photocatalytic performance than that over pristine meso/macroporous g-C₃N₄ and pristine g-C₃N₄. Based on the characterization results, it is reasonable to believe that the enhanced photocatalytic activity should be attributed to the unique meso/macroporous architecture and heterojunction structure, which results in improved mass transfer and enhances the separation efficiency of exciton dissociation. Besides, an optical simulation is initially utilized to study the optical absorption characteristics of mm-CNT since the optical absorption ability of a photocatalyst is one of the most important aspects influencing the photocatalytic ability. As a result, the enhanced ability of light absorption observed on the heterojunctions should be also favorable to achieve improved photocatalytic performances. On account of the analysis results, a possible photocatalytic mechanism for enhanced visible light photocatalytic activity is proposed.