Abstract: With the UO₂ simulated pellets prepared in our laboratory, the effects of temperature, gas composition and holding time on the process of pulverization and conversion were studied in the oxidation and reduction atmosphere, respectively. The results show that the UO₂ simulated pellets and real natural uranium pellets both have good pulverization effect by the three cycles of oxidation on air/450 ℃/4 h and reduction on φ=4%H₂-Ar/700 ℃/4 h conditions. For the treatment of the simulated spent fuel containing many fission elements, the first vol-oxidation head-end process was formed in China. Combined the three oxidation-reduction cycles process with higher temperature volatilization technology on 1 200 ℃/4 h, it can effectively remove the semi-volatile fission elements as Mo, Te, Se and Ru in the form of oxides. And the removal rates can reach more than 85%.