By dint of unique physical/chemical properties and bio-compatibility, graphene can work as a building block for a SERS substrate and open up a unique platform for tumor cells detection with high sensitivity. Herein we demonstrate a facile system with highly enhanced surface enhanced Raman spectroscopy of graphene (G-SERS). The system consists of a reduced graphene oxide (rGO) sandwiched by silver and gold nanostructures. Due to the ultrasmall thickness of rGO, the inter-coupling between Ag and Au nanoparticles is precisely controlled and the local field enhancement has been improved to more than 70 times. Associated with the unique chemical mechanism of rGO, the hybrid system has been utilized to identify tumor cells without using any biomarkers. We believe this research will be important for the applications of rGO in cancer screening.