The invention relates to a method for preparing an ethylbenzene dehydrogenation catalyst by utilizing spherical nanometer alpha-ferric oxide as an iron source. The method comprises the following steps: mixing 50-75nm spherical alpha-ferric oxide and cerium oxide to obtain metastable suspension; slowly pouring a certain number of erbium nitrate, potassium carbonate and a mixed solution of one or two rare earth metallic oxide into the suspension; regulating the pH to be 9-12 through ammonium hydroxide to obtain heavy sizing; drying for 1-2h under the temperature of 80-120 DEG C; roasting the obtained product for 2-3h under the temperature of 300-500 DEG C to obtain a catalyst precursor; mixing the catalyst precursor and additives through proper amount of deionized water to obtain sizing; extruding the sizing into strips; drying for 3-4h under the temperature of 80-120 DEG C; and roasting for 2-3h under the temperature of 600-900 DEG C to obtain the finished product of catalyst. Accordingto the method, the preparation method of ferric oxide is improved; the spherical nanometer alpha-ferric oxide being 50-75nm in size is obtained; and meanwhile, the preparation technology of a ceriumsource is improved; the coprecipitation method is carried out to prepare Fe-K-Ce series ethylbenzene dehydrogenation catalyst, so that the catalyst is high in activity and stability.