The present invention relates to a method of preparing a cerium oxide powder for a CMP slurry and a method of preparing a CMP slurry using the same, and more particularly, to a method of preparing a cerium oxide powder for a CMP slurry and a method of preparing a CMP slurry using the same in which the specific surface area of the powder is increased by preparing a cerium precursor, and then decomposing and calcinating the prepared cerium precursor. The pore distribution is controlled to increase the chemical contact area between a polished film and a polishing material, thereby reducing polishing time while the physical strength of powder is decreased, which remarkably reduces scratches on a polished film.