The invention discloses ground calcium carbonate for rare earth separation and saponification and a preparation method of ground calcium carbonate. The ground calcium carbonate for rare earth separation and saponification is characterized in that the acid non-soluble substance content is smaller than or equal to 0.5%, the effective calcium content is larger than or equal to 98.5%, whiteness is larger than or equal to 95%, fineness range D97 is 2-20micron adjustable narrow particle size distribution, specific surface area is larger than or equal to 1.5m<2>/g, and an oil absorption value is smaller than or equal to 40mL/100g. The parpearation method of the ground calcium carbonate includes raw ore crushing, dry grinding, grading, deironing, wet grinding, drying, secondary grading, tertiary grading, secondary deironing and depolymerization. The ground calcium carbonate for rare earth separation and saponification has advantages of high purity, low silicon, low ferro-aluminum, ultra-fineness, large specific surface area and narrow particle size distribution, the problem of exceeding of ammonia nitrogen ion and sodium ion contents in wastewater can be solved while occurrence of a thirdphase at an organic phase and aqueous phase interface is effectively inhibited, organic phase loss is reduced, production cost is saved, rare earth separation efficiency can be improved, and requirement of a novel rare earth extraction process can be well met.