The invention discloses a preparation method and application of modified nano calcium carbonate, and belongs to the technical field of preparation of modified calcium carbonate. Synthesis of the modified nano calcium carbonate comprises the following steps that calcium carbonate crystal whiskers are put into a vacuum oven at 105 DEG C to be dried for 2 hours, so that the water content is between 0.3-0.6%; a macromolecular modifier ABM is diluted by using an acetone solvent, and a mixed solvent is obtained after uniform mixing; the dried calcium carbonate crystal whiskers are placed into a three-roller continuous modification machine, the mixed solvent is slowly added under medium-speed stirring, and the modified nano calcium carbonate is obtained after stirring is carried out for 30 min. According to the modified nano calcium carbonate, carbon oxygen bonds with stable performance can be introduced on the surface of filler, and in the high-temperature thermal aging process, the modifiednano calcium carbonate can be added into lubricating grease by scarifying the carbon oxygen bonds in molecules to protect other chemical bonds in the lubricating grease, so that the aging speed of alubricating grease system is reduced, and the high temperature resistance is improved.