Currently, alkali is made mainly by using an ion membrane electrolysis technology in industry, and mainly adopted raw materials include industrial brine, salted bittern and whole bittern. Due to the particularity of ionic membrane caustic soda production, brine is always recycled and not discharged to the outside, and some ions can not be processed by existing primary brine and secondary brine, over time, ion concentration is formed, and causes serious influence on the current efficiency and the service lives of ionic membranes. Especially, iodine ions exist in large-molecular-weight Na3H2IO6 and Ba3H4 (IO6) 2 forms in the process of electrolysis, so that the iodine ions block an ionic membrane channel so as to hinder the passing of sodium ions, thereby reducing the current efficiency, and shortening the service lives of ionic membranes. The ionic membranes are expensive, so that the frequent replacement of the ionic membranes is adverse to the benefits of factories. Therefore, removing iodine in brine is the most economic and effective measure. According to a method for removing trace iodine in chlor-alkali brine by using ozone, disclosed by the invention, ozone is taken as an oxidant and iodine blowing for gas removal is implemented, so that iodine in brine is removed in one step, no impurity is introduced, and no pollution is caused. The method is simple in operation, high in efficiency and low in energy consumption, and can remove most of iodine in brine, therefore, the method has obvious application advantages.