The invention discloses a Schiff base magnesium organometallic compound, and a preparation method and an application thereof. The preparation method comprises the following steps: 1, heating and refluxing 2,4,6-tri-tert-butylaniline, 3,5-di-tert-butylsalicylaldehyde and p-toluenesulfonic acid in ethanol until reaction is completed to precipitate a large amount of pale yellow crystals which are 2-(2,4,6-tri-tert-butyl)-3,5-di-tert-butyl Schiff base; 2, respectively reacting the 2-(2,4,6-tri-tert-butyl)-3,5-di-tert-butyl Schiff base and 2-(2,6-di(diphenylmethyl)-4-isopropyl)-3,5-di-tert-butyl Schiff base with methylmagnesium iodide under waterless anoxic conditions to obtain a large amount of colorless crystals which are 2-(2,4,6-tri-tert-butyl)-3,5-di-tert-butyl Schiff base magnesium metal compound and 2-(2,6-di(diphenylmethyl)-4-isopropyl)-3,5-di-tert-butyl Schiff base magnesium iodide respectively; and 3, reacting the 2-(2,6-di(diphenylmethyl)-4-isopropyl)-3,5-di-tert-butyl Schiff base magnesium iodide with metallic sodium to obtain pale yellow crystals which are 2-(2,6-di(diphenylmethyl)-4-isopropyl)-3,5-di-tert-butyl sodium magnesium bi-metal compound.