Novel ternary carbon quantum dots (CDs)/Bi2MoO6 (BMO)/graphitic carbon nanofibers (GNFs) composites (CDs/BMO/GNFs) were prepared by a facile hydrothermal method and studied for use as photocatalysts. The morphological, structural and physicochemical properties of the as-prepared photocatalysts were examined in detail; that the CDs-decorated BMO particles anchored on the surfaces of modified GNFs to form heterojunctions. The photocatalytic activity of the resultant CDs/BMO/GNFs was superior for the degradation of three different organics, including Rhodamine B (RhB), methylene blue (MB) and phenol, as well as the reduction of a heavy metal ion Cr(VI), when compared with the corresponding binary composites (BMO/GNFs and CDs/BMO) and pure BMO. Our study revealed that the photocatalytic performance of ternary composite CDs/BMO/GNFs was significantly affected by the loadings of CDs or/and GNFs in BMO. Especially, the optimized sample C5/BMO/GNF-0.2, which was synthesized with a Bi/C molar ratio of 0.2 and the addition of 5 mL CDs, exhibited the best activity in the photocatalytic degradation of RhB. It was found that 99.4% of RhB was removed after 70-min exposure to the simulated solar light irradiation. This was attributed to the synergistic effects between components (CDs, BMO and GNFs) and heterojunctions, resulting in an efficient spatial separation of the photo-generated electrons and holes. A possible photocatalytic mechanism of C5/BMO/GNF-0.2 was proposed that the photogenerated holes, O-center dot(2-) and (OH)-O-center dot radicals contributed to the photocatalysis, which was supported by the radical quenching experiment and electron spin resonance analysis.