Compared to free Au nanoparticles, about 2-fold enhancement in SERS for the complex substrate of graphene-supported Au was observed via theoretical simulations. With the excitations of incident light, SERRS will play a more important role, giving an enhancement factor up to 10-100 for the supported Au compared to isolated Au. Electrons will transfer from graphene to Au and intend to gather on the upper surface of Au nanoparticles, strengthening both EM and CM. Meanwhile, the transferred electrons could raise the 6s orbital energy level of Au clusters up, increasing the probability for charge transfer from metal to probe molecules. (C) 2013 Elsevier B. V. All rights reserved.