The invention discloses a method for preparing nanometer calcium carbonate, comprising the steps as follows: the raw material quicklime or Calcium Hydroxide is added in water to prepare suspending liquid of 8 to 12 percent, and mixed fully; while mixing, mixed carbon dioxide / air gas containing 28 to 30 percent carbon dioxide is fed to perform carbonization reaction, wherein, the gas feeding rate is 3 to 10 liter per minute, and the absorptivity constant of the carbon dioxide is controlled to 0.7 to 2.5 per second, the temperature in the whole carbonization process is 28 to 40 DEG C, and the reaction is stopped until the PH value of the suspending liquid declines to between 6.8 to 7.2; the suspending liquid is filtered and injected into two X-shaped channels which are ready, the calcium carbonate particulate is adjusted to a nanometer collider in diameter of 20 to 80 nanometer for splitting, emulsifying, dispersing, and synthesizing the nanometer calcium carbonate solution. The invention has the advantages of simple technique and method, good product quality, good stability, convenient operation and low cost, is applicable for the middle-sized and small-sized enterprisers involving in the industries including rubber, paint, plastic, printing ink, medicine, food, and health care product, etc.