The corrosion behavior of copper-nickel-tin alloy in seawater with and without SRB has been tested by electrochemical techniques, SEM micrographs and EDX spectra. The geometric and electronic structure and active sites of Cu-n, Cun-1Ni and Cun-1Sn (n <= 9) clusters have been studied using DFT. The results indicated nickel and tin preferred to be the surface or outer layer in copper alloy, formed an oxide film on surface, then alloy would be corroded to Cu2O mostly after immersion. The corrosion process was accelerated in the presence of SRB, the mainly corrosion product was Cu2S, which was less protective for alloy. (C) 2011 Elsevier B.V. All rights reserved.