Defective oxygen vacancy aiming at surface self-modification for target materials is proved to be highly efficient for catalysis. Here, we reported in situ implantation of Ti3+ ions in TiO2/graphene quantum dot nanosheets (Ti3+-TiO2/GQDs NSs) as an efficient visible-light photocatalyst, using a facile sythesis of two-step calcination. By virtue of heat treatment for TiO2 nanosheets and carbon source of citric acid, significant oxygen vacancy/Ti3+ sites can be introduced in TiO2/GQDs NSs via carbothermal reduction reaction derived by GQDs, which contributed to provide critical active sites for photocatalysis. Such nanohybrids exhibited extented optical absorption in visible-light region and low recombination of photo-induced carriers. The photodegradation of methylene blue (MB) and rhodamine B (RhB) result both demonstrated higher visible-light photocatalysis performance than that of original TiO2. Based on the analysis of experimental results, oxygen vacancy/Ti3+ sites and GQDs induced in TiO2 nanosheets play a synergistic effect for the improvement in photocatalysis properties. Finally, the formation mechanism and deep understanding for the carbothermal reduction induced Ti3+ sites is provided in DFT analysis.