The invention relates to a preparation method of a micropowder weighting agent of ultra high density for drilling fluid and an application thereof. The micropowder weighting agent of ultra high density comprises the following components in parts by weight: 70-90 parts of a weighting agent, 15-30 parts of an organic solvent, 20-30 parts of an aqueous solution, 2-7 parts of a surfactant and 5-9 parts of a cosurfactant. The main chemical component of the weighting agent of the present invention is iron powder or compound of iron, the weighting agent density is higher than 6.5g/cm<3> and the specific gravity is far higher than that of barite powder and routine weighting agents used at present, the particle size D90 is smaller than 35 [mu]m; the weighting agent has a granule type and appearance which is similar to a spherical shape, and has good dispersibility and suspensibility; the weighting agent has a good compatibleness with the drilling fluid, and the drilling fluid of ultra high density prepared by the weighting agent has good rheological property and stability, thereby satisfying requirements of deep well and complex well to the drilling fluid of ultra high density.