Photocatalytic reduction of CO2 by semiconductors is of great significance in generating value-added fuels. Here, we construct a novel S-C-S heterojunction constituted of MoS2/SnS2/r-GO by a simple solvothermal method. The prepared MoS2/SnS2/r-GO showed significant photoexcitation of photosensitive oxygen (ROS) by electron spin resonance spectroscopy, demonstrating that superoxide radicals (•O2-), pores, and hydroxyl radicals (•OH) are the main active species. The constructed S-C-S heterojunction has a multilevel electron transport mechanism and synergistic effect, which provides the possibility of producing more organic fuel. The photocatalytic materials were characterized by XRD, XPS, SEM, TEM, PL, etc. As a result, the atomic layer MoS2/SnS2/r-GO heterojunction exhibited a CO formation rate of 68.53 μmol g-1 h-1 and a CH4 formation rate of 50.55 μmol g-1 h-1, respectively. This work opens up new prospects for the formation of heterojunctions of chalcogenide transition-metal sulfides.