Non-noble metals such as Ni, Bi, Co, Cd and Sn are considered as promising cocatalyst in photocatalytic field. Herein, by utilizing the oxide g-C3N4 with plentiful hydroxyl and carboxyl groups as a basic block, Sn/oxide g-C3N4 composites were constructed by a facile electrostatic self-assembly strategy followed by a chemical reduction method. The as-prepared Sn/oxide g-C3N4 catalyst exhibit remarkably improved visible-light-driven photocatalytic performance toward degradation of methyl orange (MO) and phenol compared with oxide g-C3N4 due to the facile interfacial charge separation, as evidenced by the photoluminescence and transient photo-current studies. The work function measurements revealed the photo-generated electrons in the conduction band of oxide g-C3N4 could be trapped by metallic Sn and the band bending in the space-charge region of the Sn/oxide g-C3N4 composite further promoted the separation of electrons and holes, which are responsible for the enhanced photocatalytic performance. Moreover, O-center dot(2)- radicals are found to be the predominant species toward degradation of MO, while holes (h(+)) are the most critical species for the degradation of phenol, as proved by the active species trapping experiments and ESR technique measurements. The present study provided a new insight into the design and fabrication of oxide g-C3N4 based hybrid photocatalysts with reasonable electronic structures for photochemical reactions.