Rapid recombination of photoexcited carriers has always been a severe problem that inhibits photocatalytic activity. Designing two-dimensional (2D) heterostructured nanocomposite using layer material is regarded as an effective method to obtain advanced photocatalyst. In this work, we designed novel 2D/2D porous graphitic C3N4/SnS2 (Pg-C3N4/SnS2) composite by in-situ growth of SnS2 onto Pg-C3N4 sheets. The 2D Pg-C3N4 nanosheets were coupled with 2D SnS2 nanosheets forming a large-scale contact interface, leading to high efficient interfacial charge transfer efficiency and shortening the distance of charge transmission. According to the experiments, the optimized Pg-C3N4/SnS2 composite exhibits the highest apparent pseudo-first-order rate constant k(app) of 0.14321 min(-1) with the content of 10% Pg-C3N4, which exceeds the rates of pure Pg-C3N4 and SnS2 for approximately 18 and 8 times, respectively. On the basis of radical-trapping experiment and band structure analysis, we confirm that the Z-scheme heterojunction was formed between SnS2 and Pg-C3N4. The electrons in SnS2 CB transfer and combine with the holes in the Pg-C3N4, which is beneficial to the spatial separation of photoinduced carriers and strengthen the redox capacity of the photocatalyst. This work supplies an efficient way to design 2D/2D heterojunction for the photocatalytic application.