In this work, the Pt/CeO2 catalysts with different calcination temperatures have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in the sulfur-iodine cycle at various temperatures. The Pt/CeO2 catalysts strongly enhance the decomposition of HI to H-2 by comparison with blank yield, especially the catalysts calcinated at high temperature. TG-FTIR, BET, XRD, TEM, and TPR were performed for catalysts characterization. Platinum was introduced into ceria to form the Pt/CeO2 catalysts by sol-gel. It was found that, through the sol-gel method, the Pt ions could be inserted into the ceria lattice. This brought about a different synergistic effect between the Pt and Cc components, such as increase of the oxygen mobility in ceria support and improvement of the thermal stability of catalyst. According to a so-called "self-regeneration" model and the results of XRD and TPR, a similar mechanism is supposed to exist in the Pt/CeO2 catalysts synthesized by sol-gel at high calcination temperature. It involves the complex conversion such as Ce4+ + pt <-> Ce3+ + pt(2+) and oxygen-vacancy diffusion in the Pt-Ce-O system.