MgO nano-particles are prepared by ultrasonic cavitate, and-Fe2O3 nano-particles are prepared by chemical precipitation method, then MgO and-Fe2O3 are mixed in a beaker. After the ultrasonic dispersion for 2 h, MgO/-Fe2O3 admixture is calcined at 400℃ to synthesize MgFe2O4 nano-particles. TEM and XRD tests show that MgFe2O4 takes on a spinel structure and the particles sizes range from 20 to 30 nm. The theoretieal analysis indicates that the ultrasonic cavitate effect enhances the reaction activity of raw material, augmentes specific surface area and the contact area of reactant, which can promote reaction rate, reduce reaction temperature, and make possible the chemical reaction that is difficult to complete in common condition.