Fe2O3@NC composites with different crystal forms were prepared in situ derived from biomass and Fe(NO3)3 by one-pot synthesis. In the process, biomass played important role in guiding the formation of γ-Fe2O3 beside the source of the graphene like nanosheets including N, C, O elements (NC). When the mass ratio of biomass and Fe(NO3)3 is proper, both of α- Fe2O3 and γ-Fe2O3 nanoparticles with the size of 3–10 nm deposit simultaneously on the graphene like nanosheets, forming uniform Fe2O3@NC nanosheets with the thickness of 15–30 nm. The specific area of Fe2O3@NC composite is improved drastically due to the synergistic effect between Fe2O3 nanoparticles and the graphene like nanosheets, resulting in the improvement of adsorption performance. The graphene like nanosheets as supporter of Fe2O3 nanoparticles enhance the separation and transfer of electrons and holes due to its good conductivity. On the other hand, the photoinduced electrons and holes could be separated and transferred quickly due to the effect of α-γ-Fe2O3 phase junction. Under the dual effects, the photocatalytic reaction rate constant of Fe2O3@NC composite with α-Fe2O3 and γ-Fe2O3 reaches to 1.44 × 10−3 L⋅ mg−1⋅ min−1, exhibiting far higher than pure Fe2O3 and Fe2O3@NC composite with single crystal form. Moreover, Fe2O3@NC composite could be recovered by magnet owing to the strong magnetism property of γ-Fe2O3, exhibited good reusability after five cycles by magnet recovery.