Carbon quantum dots (CQDs) is a promising material for photosensitization applications but substantially suffers from the tedious product separation in solution and poor photosensitive efficiency in the visible light range. Herein, a facile and efficient hydrothermal method is utilized to assemble nitrogen-doped CQDs (NCQDs) onto graphene aerogel (GA) for reduction of toxic Cr (VI) in aqueous solution under visible light illumination. The photoactivity results suggest that GA skeleton endows NCQDs with a strongly enhanced photoactivity compared to that over blank NCQDs. Photoelectrochemical results demonstrate that the introduction of GA skeleton facilitates more efficient separation and transfer of photogenerated charge carriers under visible light irradiation. Moreover, as compared with N-free counterparts, the broadened light absorption of NCQD resulting from the ameliorated nanocrystallinity and the nitrogen dopant in graphitic structure play an important role in the reduction of Cr (VI) reaction under identical conditions. It is believed that this work could extend the promising applications of CQDs as an efficient visible-light-responsive photosensitizer for water purification and beyond.