A lower concentration of iodine (< 0.2 mg/L) in the salt water used for caustic soda production is crucial to prolong the service life of ionic membrane and decrease the cost of production. The removal of iodine from salt water by resin adsorption was carried out in this work. It was found that the existing species of iodine is the key factor to affect the adsorption, and I-2 is the optimal adsorbed species in salt water through the reaction between I-2 and Cl- in the resin to form (ClI2)(-). A simple pre-treatment method was developed to transform different iodine species in salt water into I-2 by adjusting the solution to pH 1.5-2.5 and redox potential (Eh) 530-560 mV. A novel purification system for the removal of iodine from salt water was subsequently developed and constructed based on the pre-treatment method and the adsorption thermokinetics of I-2. The stability and reliability of this developed method and system were demonstrated by a scale-up experiment to remove iodine from the refined salt water used for caustic soda production, by which the concentration of iodine can be stably decreased to far < 0.2 mg/L.