The oxygen functional groups and defects of carbon material played an important role in dispersion of active components and additives, reduction of Ce⁴⁺, etc. The reduction of Ce⁴⁺ and structure defects would increase surface oxygen concentration and oxygen vacancies. The dispersion of active components and additives, surface oxygen concentration and structure defects were key factor on CO oxidation. The oxygen functional groups and structure defects of porous carbon spheres (PCSs) increased by O₃ treatment method. The effects of O₃ treatment concentration on structures, properties of PCSs support and Pd-Ce/PCSs were investigated in detail. The particle size of PCSs had not been changed basically after O₃ treatment. However, the outer of PCSs became uneven, which was main reason of the external surface area increase. The content of surface Pd⁴⁺, surface adsorption oxygen concentration, oxygen vacancies, defects, increased with increasing O₃ treatment concentration. Relationship between the functional groups, defects of porous carbon spheres and their catalytic performance was investigated in detail. CO oxidation test showed that the Pd-Ce based catalysts supported by the PCSs after O₃ treatment concentration for 45 mgL^-1 had the best activity. The effect of moisture on CO conversion was explored, and the catalysts showed excellent stability under moisture condition.