We performed extensive DFT calculations for the microscopic mechanism of CO oxidation on cationic, neutral and anionic X-O-Cu (X = Au, Ag) clusters. We obtained following findings. First, the reaction mechanism of neutral X-O-Cu (X = Au, Ag) to the CO follows the Eley-Rideal-like (ER) mechanism and Langmuir-Hinshelwood-like (LH) mechanism. Second, as compared to the pure Au clusters, new reaction pathways have been found via a Langmuir-Hinshelwood-like (LH) mechanism. The oxidation of CO on cationic Au-O-Cu in nature follows an Eley-Rideal-like (ER) mechanism. Third, comparing with their reaction profiles between cationic, neutral and anionic Au-O-Cu and CO, all the reactions on Ag-O-Cu can occur more easily. Furthermore, the selectivity of the oxidation of CO on Ag-O-Cu will be improved. On the basis of our calculations, we suggest that AgCu may also be a good catalyst due to its high oxidation performance. (C) 2017 Elsevier B.V. All rights reserved.