Photolysis of iodine and iodine compound in the presence of O3 has been proposed as a mechanism leading to intense iodine oxide particles(IOPs) formation, which has a profound influence on global climate change and atmospheric environment. It is believed that the formation of IOPs is involved with the production and oxidation of a series of iodine oxides (IxOy). However, the details of IOPs formation are not yet resolved, and there are still important gaps between modeling and field research, or even between different modeling work, which hinders precise evaluation of IOPs’ impaction atmospheric processes, climate and human health. The main progress research on the formation of iodine oxide particles has been described and the major challenges have been discussed.