In this paper, 3D Cu-Ce-Ox catalysts with controllable pore diameters were rationally designed and synthesized by a facile hard-template method. By controlling the hydrothermal synthesis time, mesoporous silica KIT-6 with different pores were prepared. Then, the 3D Cu-Ce-Ox catalysts were synthesized by nano-replication technology with KIT-6 as hard template. These catalysts expressed 3D pore structure, possessed higher pore volume and large pores, and owned more surface active sites, which were helpful for CO oxidation. When the synthesis time of KIT-6 was 24 h, this catalyst showed the highest catalytic activity. The reason was due to its relatively stronger redox ability and surface activity species. More Ce³⁺, Cu⁺ and chemical adsorbed oxygen concentration was very useful in achieving the highest catalytic performance.