Using density functional theory (DFT), the adsorption behaviors of O, CO and CO2 over small cluster Con (n=1~7) were studied, with the focus on the adsorption structure, stability and electronic properties. The results indicate that the optimized structures of the cluster ConO adsorption site remain unchanged, and the adsorption sites of the cluster ConCO are consistent with initial structures, except for the fact of 7B1 changed to 7T2. The cluster ConCO2 varies significantly with the structure of adsorption sites (top, bridge, and hole). The adsorption energy of cluster ConA is in descending order as ConO, ConCO, ConCO2, while the changes of the energy gap are of little regularity, the adsorption stability of cluster ConA, the distance between Co and O(C), the length of C—O bonds, and the charge transfer all show regular changes, indicating that the adsorbents are activated. The oxidation mechanism of cluster Co2 oxidizing CO shows that path b only needs to cross the barrier of 0.436 eV and path a requires 1.686 eV, indicating that path b is more favorable. The cluster Co2OT is expected to be a good CO oxidation catalyst.