The invention relates to a method for preparing a nanometer magnesium ferrite material, and concretely relates to a method for preparing nanometer magnesium ferrite through utilizing active e magnesium oxide as a raw material. The method which treats light burning powder (the active magnesium oxide) and iron chloride as raw materials comprises the following steps: 1, stirring iron chloride hexahydrate (FeCl3.6H2O) at normal temperature for dissolving to prepare an aqueous solution; 2, carrying out a hydration reaction of the light burning powder under conditions comprising ultrasonic power, a stirring rate, a reaction temperature, a reaction time and the like; 3, adding the iron chloride solution obtained in step 1 to a (light burning powder) emulsion in a dropwise manner at a rate under conditions comprising ultrasonic power, a stirring rate, a reaction temperature, a reaction time and the like for carrying out an association reaction; and 4, filtering, washing and drying the obtained micro-emulsion; and 5, calcining the obtained magnesium ferrite precursor to obtain a brown-red solid. The method has the advantages of simplicity, mild reaction conditions, no pollution, and low cost.