A research has been conducted on the geometric structure, stability, electronic properties and adsorption reaction behaviors of Coqn(n =1~5, q=0, +, -) clusters and atomic oxygen adsorbed on the clusters by using the generalized gradient approximation PBE functional of Dmol3 program based on density functional theory (DFT). The results indicate that the structure of Coqn clusters remains unchanged, while the average binding energy of the cationic cluster (Co+n) is much higher than that of neutral clusters (Co0n ) and anionic clusters (Co-n), due to the fact that the loss of an electron can significantly enhance the stability of the cluster. The adsorption stability, the Co—O bond length and the charge transfer of atomic oxygen at the top site, bridge site and hole site of Coqn clusters show regular changes, which indicates that atomic oxygen is activated. When the adsorption energy of the Co-4O B cluster is -8.375 eV, the orbital analysis shows further that the 2p orbitals of atomic oxygen and the 3d orbitals of cobalt are hybridized, with an interaction a chemical adsorption.