A series of iron oxide catalysts prepared from ferric/ferrous mixed salts were studied to explore the structure-performance relationship for CO2 hydrogenation. The high selectivity to C5+ hydrocarbons (47 %) at a high CO2 conversion (34 %) could be maintained when the initial Fe3+/Fe2+ ratio in preparation varies from 2/1 to 2.5/0.5, while both the CO2 conversion and selectivity to C5+ hydrocarbons show an obvious decline as the ratio deviates from the range. Combined with various characterization results, the volcano-like evolution of CO2 conversion and selectivity to C5+ hydrocarbons is related to the structure and phase transition of the iron oxide catalysts. With the increase of Fe3+/Fe2+ ratio, the catalyst composition gradually changes from Fe3O4 nanoparticles to beta-FeOOH nanorods, meanwhile, the size of Fe3O4 nanoparticles decreases. The smaller Fe3O4 nanoparticles could provide higher active surface area for improved reducibility and CO2 adsorption capacity, whereas the presence of beta-FeOOH nanorods is not favorable for the reduction and carburization of catalysts. Consequently, the variation of initial phase composition and structure would affect the formation of Hagg iron carbide (chi-Fe5C2) phase during reaction, which has decisive effect on higher hydrocarbons synthesis from CO2 hydrogenation.