Graphene quantum dots (GQDs) interacting with MoS₂ monolayers induce an effective photo-excited charge transfer at the interface. Both the photoluminescence (PL) and valley polarization of this GQDs/MoS₂ heterostructure can be modulated under various doping charge densities. Photon-exciton interaction theory was successfully used to explain and calculate the heterostructure PL control, and further applied to the valley polarization tuning.