Volatile radionuclides generated during the nuclear fission process, such as iodine, pose risks to public safety and cause the threat of environmental pollution. Covalent organic framework (COF) materials have a controlled pore structure and a large specific surface area and thus demonstrate great opportunities in the field of radioactive iodine adsorption. However, the harsh synthetic conditions and the weak binding capability toward iodine have significantly restricted the applications of COFs in iodine adsorption. Here, we demonstrate a facile way to prepare a series of stable C-N-linked COFs with high efficiency to capture radioactive iodine species. Large-scale synthesis can be conducted by the aldol condensation reaction at room temperature. The resulting COFs have a large surface area and a strong resistance to acid, base, and water. Moreover, all types of COFs show high iodine adsorption, up to 2.6 g/g (260% in mass), owing to the large surface area and the functional groups in COFs. They not only absorb conventional I2 molecular but also ionic state (I3 - and I+) iodine species. Theoretical calculations are further performed to understand the relationship between different iodine species and the functional groups of all COFs, offering the mechanisms underlying the potent adsorption abilities of COFs.