Abstract: ¹³¹I is an important radioisotope in nuclear medicine, but due to the inherent defects of wet separation technology，the separation of 131I from uranium fission products (UFPs) has serious environmental pollution and low extraction efficiency. Considering the high yield of ¹³¹I in UFPs, it is necessary to develop a new method for separating ¹³¹I from UFPs, because it can not only expand the ways to obtain ¹³¹I, but also improve the utilization efficiency of UFPs. Unlike the traditional wet chemical separation technique, ¹³¹I was separated from UFPs by dry distillation in present work. Three stages worked under different temperatures, such as powdered the target, dry distillation and heat preservation, were involved in the separation process, so as to acquire as much as ¹³¹I from the target. The effect of dry distillation temperature on ¹³¹I separation efficiency was systematically investigated, it was found that the separation efficiency of ¹³¹I was higher than 98% when the distillation temperature was over 950 ℃. Moreover, it was also observed that both radioiodine and ¹⁰³Ru were sublimated from the UFPs at the optimum distillation condition, but only radioiodine existed in the product. In order to explain this phenomenon, a detailed analysis of the iodine separation process was carried out. By combining the experimental results with the theoretical calculations, the separation mechanism of radioiodine from ¹⁰³Ru was estimated as: ¹⁰³Ru volatilized from the UFPs through the formation of RuO₄, the volatile compound of ¹⁰³Ru may be decomposed into RuO₂ during the migration because of the high temperature in the heating tube, and then settled down. Therefore, to separate ¹³¹I from UFPs by dry distillation and obtain ¹³¹I product with high radiochemical purity, it is necessary to rationally plan the separation process, at the same time, the scientifically design of the heating tube length is also meaningful.