With SnCl4·5H2O and graphene oxide as raw materials and aqueous solution of ethanol as the solvent, we have prepared SnO2 quantum dots (diameter about 3-5 nm)/graphene nanocomposites using a facile hydrothermal method in one step, and solved the reunion of quantum dots successfully. The visible-light-driven photocatalytic efficiency of SnO2 quantum dots depends to a great extent on their dispersity. Because of the large-sized two-dimensional surface, the graphene sheet could behave as a solid support for quantum dots through interfacial interaction to avoid particle aggregation. Composites of SnO2 quantum dot/graphene show a great photocatalytic performance in visible light, and the morphology and structure of the product are characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared Spectrometer (FT-IR) and other techniques. The optical properties are investigated by using UV-visible (UV-vis) absorption spectrum. Additionally, the photocatalytic activity of the product is measured by the degradation of rhodamine-B dye solution in visible light. Results show that the preparation of samples with high catalytic activity in visible light, the shift in the optical response of composites may produce a positive effect on the improvement of photocatalytic efficiency in UV to visible spectral range Moreover, owing to its special π-conjugation structure, large specific surface area as well as high conductivity, graphene can enhance the photocatalytic activity. Compared with the pure SnO2, pure graphene catalytic performance is greatly improved in visible light, its excellent photocatalytic activity is due to the combination of strong absorption and effective separation of photogenerated carriers in the samples. Finally, the formation mechanism of the composite and its photocatalytic mechanism are studied.