The effective capture of radioactive vapor waste during fission is of great significance to the safe utilization of nuclear energy. Covalent organic frameworks (COFs) are a kind of novel porous crystal polymers, with highly flexible channel structure and molecular designability. COFs containing nitrogen-rich structures and flexible units can provide effective binding sites for adsorption of iodine, and are potential adsorption materials. In this study, the fully flexible s-triazine-based COFs were prepared by one-pot condensation using fully flexible building blocks of 2,4,6-tris(4-formylphenoxy)- 1,3,5-triazine (TPT–3–CHO) as a knot and ether-based diamines as flexible linkers. The three fully flexible s-triazine-based COFs have large surface areas (1490, 1596, and 1657 m² g⁻¹), good crystallinity and outstanding adsorption capacitiy of volatile iodine (4.10, 4.13 and 3.40 g g⁻¹) with excellent recyclability. As the linker lengths increase, the specific surface areas increase, but the adsorption amounts of iodine decrease. Moreover, the fully flexible s-triazine-based COFs also have high sensitivities for fluorescence detection against p-nitrophenol and iodine. Their quenching constants (K_SV) for p-nitrophenol are 5.59 × 10⁴, 4.05 × 10⁴ and 2.35 × 10⁴ L mol⁻¹, respectively. The fully flexible s-triazine-based COFs have larger specific surface area, high iodine adsorption, and more sensitive fluorescence sensing performance than the COFs formed by the corresponding rigid linkers.