The structural and magnetic properties of CoO were investigated by both first-principles and experimental studies. The results of first-principles calculations indicate that the spin splitting induced by oxygen vacancies can lead to the net moment in the CoO. The density of states of CoO shows a band gap of 2.2 eV, while the impurity states appear with the oxygen vacancies. Furthermore, the CoO films with oxygen vacancies were grown on MgAlO and SrTiO substrates by using reactive sputtering. The structural analysis reveals that the CoO films are epitaxial. Consistent with the first-principles study, magnetism is observed in the CoO films, which attributes to the oxygen vacancies influencing spin structure by superexchange interaction.