Abstract: Nowadays, fast breeder reactor (FBR) is one of the preferred reactor types for Generation Ⅳ advanced nuclear energy systems in the world. FBRs can improve the utilization rate of uranium resources, make the long-lived spent fuel generation much lower, and achieve the minimization of radioactive waste. The characteristics of high burnup, high irradiation, and high plutonium content of fast reactor spent fuel make it difficult for the traditional aqueous reprocessing process to meet the separation needs. Compared with the traditional liquid separation technology, dry technology has potential advantages and dry reprocessing is mainly under high temperature argon environment, for the treatment of radioactive gases in the spent fuel reprocessing process, as the ¹²⁹I containing exhaust gas has attracted much attention due to its long half-life, high content and high toxicity. In this paper, Bi(NO₃)₃·5H₂O was used as the source of bismuth, L-cysteine as the source of sulfur, and ethylene glycol as the solvent, two-step hydrothermal method was used to prepare bismuth sulfide modified zeolite composites (Bi₂S₃-MOR). The static adsorption experiments were carried out in a reactor with a valve, where the composites were first placed in a polytetrafluoroethylene liner together with iodine (methyl iodide), and the experiments were kept in an argon environment by closing the valve after 20 min of argon gas was passed through the valve. The physical phase of the composites was analyzed by XRD, the specific surface area and pore size by BET, the structure of functional groups by FT-IR, the morphology of the materials before and after modification and the distribution of the elements by SEM and EDS, the loading after modification by ICP-OES, and the content of C and H in the composites by elemental analyzer, and the valence change of the composites before and after the adsorption as well as the strength of the binding energy were analyzed by XPS, the thermal stability of the composites was analyzed by TGA. The experimental results show that the static adsorption capacity of bismuth sulfide modified zeolite for monosubstituted iodine is up to 180 mg/g at 130 ℃ under argon environment, and the trapping forms are both chemisorbed BiI₃ and physisorbed I₂, while the static adsorption capacity for CH₃I is 50 mg/g at 50 ℃ under argon environment, and only the chemical adsorption in the form of BiI₃ exists. The research results can provide new ideas and options for the purification and treatment of gaseous radioactive iodine in the dry reprocessing process.