The behaviors of atmospheric 129I and the global 129I cycle remain incompletely understood because the spatiotemporal resolution of monitoring is insufficient, and few measurement-based models have been reported. This study aims to quantitatively understand the global 129I budget. When quantifying, we conducted global atmospheric 129I dispersion simulations covering from the period 2007 to 2010. To achieve this goal, the present study newly incorporates the iodine chemical processes of two gas-phase chemical reactions, six photolysis reactions, and two heterogeneous reactions into an existing atmospheric 129I transport model (GEARN–FDM). In addition to the aerial release of 129I from nuclear fuel reprocessing facilities, the model includes the volatilization processes of 129I compounds from the Earth’s surface. The net 129I exchange fluxes from the atmosphere to the Earth’s oceans and land were estimated to be 5.3 GBq/y and 18.0 GBq/y, respectively. The global 129I emission from the oceans was estimated as 7.2 GBq/y, and nearly half of the emission totals are emitted from the English Channel (3.2 GBq/y). In addition, the global 129I emissions from land are estimated to be 1.7 GBq/y. The remarkable 129I emission levels from land mainly appear in Europe, Russia, and North America, and the emission distribution is impacted by the activities of past and ongoing nuclear fuel reprocessing facilities. The total 129I emissions from the oceans and land are lower than the 129I emissions from the model-included nuclear fuel reprocessing facilities (23.3 GBq/y), and show that the aerial releases from the nuclear fuel reprocessing facilities in operation are still important 129I sources.