Methyl iodide (CH3I), a common fine chemical intermediate used in the production of pesticides and pharmaceuticals, is characterized by both acute and chronic toxicity. This study presents a novel approach for the purification of radioactive CH3I by utilizing microchannel reactor. Microchannels with various structures are fabricated on a metal substrate using laser technology, and two-step impregnation method is employed to construct microchannel reactors. Small-scale experiments are conducted to investigate the effects of different microchannel structures (rectangular, polyline, and wave), adsorbent content, and working conditions on the adsorption performance of CH3I. The results indicate that the wave microchannels have higher adsorption efficiency of CH3I and stable adsorbent coating performance. Through SEM and XPS technology analysis, the further CH3I adsorption mechanism is discussed in depth. From the overall results, we obtain that CH3I is captured by microchannel reactor to produce silver iodide, which belongs to chemisorption behavior. The mass transfer of microchannel reactor is investigated, and a new correlation of Sherwood number is proposed based on data for the adsorption experiments of CH3I. The numerical model is developed to simulate the performance of microchannel reactor, which is verified by the experiments.