In this paper, a high cost-performance surface-enhanced Raman scattering (SERS) flexible substrate is demonstrated, which endowed with excellent optical transparency, high SERS activity and large scale. This SERS flexible substrate of Ag/Cu/Polyethylene Terephthalate (PET) was prepared by replacing Cu atoms with Ag atoms in situ on Cu nano-film. The Ag/Cu/PET flexible substrate shows high sensitivity in SERS detection and the minimum detected concentration of R6G can reach 10(-10) M. In addition, the residual methylene blue (MB) on a fish surface was selected as the analyte, the results no doubt shows the potential of SERS technology application in food detection. (C) 2016 Elsevier B.V. All rights reserved.