Porous carbon spheres (PCSs) were synthesized by surfactant assisted-hydrothermal method and the oxygen functional groups and structure defects of PCSs were controllably modulated by O₃ treatment technology. Especially, the treated time and temperature played the significant roles in this strategy. Notably, the SEM indicated that the morphology and particle size of PCSs had not been changed basically after O₃ treatment. However, the specific surface area of PCSs decreased with increasing O₃ treatment time at 100 ℃ and increased with increasing O₃ treatment temperature at 15 min. The effects of oxygen functional groups and structure defects on the activity of Pd-Ce/PCSs were tested in detail. A series of characterizations showed that particle size, the content of surface Pd⁴⁺, surface adsorption oxygen, oxygen vacancies, and structure defects obviously increased after O₃ treatment. The increased content of surface Pd⁴⁺, surface adsorption oxygen, oxygen vacancies, and structure defects were advantageous to the improvement of activity, but the enlarged particle size was disadvantageous. Therefore, the O₃ treatment temperature and time is vitally significant for the effective regulation of active sites of PCSs surface. Besides, the effect of moisture on CO conversion was also investigated, and the optimal catalyst showed excellent stability under moisture condition.