All-solid-state batteries have been expected to overcome the safety problem of present lithium-ion batteries including organic liquid electrolytes. The materials with high ionic conductivity are urgently needed. In this paper, we reported a new ionic crystal Sr2Fe8O18 which can be applicated on solid electrolyte. Sr2Fe8O18 is a typical p-type semiconductor and shows a layered monoclinic crystal structure. The resistivities of Sr2Fe8O18 in the temperature range of 20 ~ 145 °C were above 107 Ω•cm. The microstructure of Sr2Fe8O18 was flaky, and the size of flaks were 1 µm ~ 5 µm. The E- P curve suggested that it was a ferroelectric semiconductor and had small ferroelectric effect. The dielectric response study (Cole-Cole plot) showed that Sr2Fe8O18 had two separated relaxation time, each of which contained a group of relaxation. The ionic conductivity σ of the sample was calculated to be 0.2196 × 10− 4 S/cm. The conductive mechanism which confirmed by the results of First principle calculation at 300K is mainly sublattice vacancy cation diffusion with self-diffusion coefficient D of 1.794 × 10− 5cm2/s. Fe ion has two dimensional diffusion path (x and y axial), and Sr ion has on dimensional diffusion path (x axial). The crystal structure of Sr2Fe8O18 shows tremendous potential application on the solid electrolyte preparation.