Abstract: Toxic volatile organic compounds (VOCs) pose significant hazards and pollution to human health, organisms, and the environment. Photocatalytic technology is an effective method for degrading and eliminating VOCs. Formaldehyde is a common VOC, and its degradation and elimination are very important for human health. Cerium and Silicon co-modified titanium dioxide (CST) was prepared by a solvothermal method, which exhibited superior photocatalytic degradation performance of formaldehyde. This is attributed to the significant increase in specific surface area due to silicon doping into the titanium dioxide lattice, which generates more surface acidic sites and improves the adsorption and activation performance of formaldehyde; the presence of surface silicon significantly increases the amount of surface hydroxyl groups, thereby improving the performance of photocatalytic generation of hydroxyl radicals. Cerium modification changes the valence band structure, expanding the absorption range to the visible light region, but also improves the separation efficiency of photo generated charge carriers. The selective generation of hydroxyl radicals with stronger oxidation ability in photocatalytic formaldehyde degradation was achieved through the regulation of photocatalyst chemical composition.