Abstract: Iron oxides were nonstoichiometric chemical compounds. Their reduction processes were remarkably influenced by nonstoichiometries. Dieckmann's defect model of magnetite and Weiss's ideal solid solution model of wustite were adopted to analyze the thermodynamic influences on the reduction processes. The dependences of deficiency degree δ on weight loss and Fe²⁺ mole ratio were analyzed by using the charge conservation and mass conservation principles. These relationships were recommended to judge the final product of the reduction processes. According to theoretical analyses and calculations,the predominance area diagrams including different nonstoichiometries of magnetite and wustite were determined in equilibrium with the reduction potentials P_CO(H2) at different temperatures. It comes to a conclusion that when the reduction weight loss ratio is less than 6%(without metallic Fe),magnetite is predominant in the pure hematite reduction at a certain temperature and reduction potential; but when the reduction weight loss ratio is higher than 6%,the process then enters the zone of wustite.