In this paper, the mean grain diameters of nanomaterial Fe2O3 are determined by X-ray diffraction. The measurements of positron lifetime have been performed. The annealing temperature dependence of D and the short lifetime component τ1, intermediate lifetime component τ2 and their intensity ratio Ｉ2／Ｉ1 as function of D are given. The interface construction of nanomaterial Fe2O3 as well as the corresponding relationship between mean positron lifetime τ and S-parameter of Doppler broadening spectrum are discussed.