The invention provides a method for preparing nano calcium carbonate. The method comprises the following steps: introducing carbon dioxide gas into a carbonization reaction tower; spraying an atomized calcium hydroxide solution into the carbonization reaction tower by virtue of a fine slurry pump to ensure that the calcium hydroxide solution performs carbonization reaction with the carbon dioxide gas so as to generate calcium carbonate turbid liquid boiled slurry; and keeping the pressure of the carbonization reaction tower by introducing the calcium carbonate turbid liquid boiled slurry into a boiled slurry tank, controlling the quantity of the carbon dioxide gas introduced into the carbonization reaction tower, and controlling the quantity of the sprayed calcium hydroxide solution. By adopting the method for preparing nano calcium carbonate provided by the invention, nano calcium carbonate of types such as cube type, chain type and delta type in a particle size range of 10-100nm can be prepared. Moreover, production equipment is simple in structure and easy to maintain, the production cost is relatively low and the yield is relatively high; therefore, the method can be economically and massively used in the industry.