Ag-Zr alloy films were deposited on flexible polyimide (PI) substrates by magnetron sputtering and subsequently subjected to vacuum annealing. Effects of annealing temperature, Zr content and film thickness on formation of Ag particle and the surface enhanced Raman scattering property of Ag particles/Ag-Zr alloy films have been investigated. Results show that microstructure of Ag-Zr alloy film changes significantly after annealing and a large number of regular polyhedral Ag particles spontaneously formed on the surface of annealed Ag-Zr alloy films. The Ag particles are single crystal and uniformly distributed on the Ag-Zr alloy films surface to form the Ag particles/Ag-Zr alloy films composite structure with large specific surface area. The detection limit of R6G concentration using Ag particles/Ag-Zr alloy films covered by 12 nm Ag film as SERS substrate is significantly lower than 5 x 10(-8) M (1 M = 1 mol/L) due to its abundant active "hot spots". The particle/film composite structure obtained in this paper provides a method to prepare the highly efficient SERS substrates.