NOVELTY - An ultrafine calcium carbonate is prepared by stirring calcium carbonate, ammonium bicarbonate, water, and sodium dodecyl sulfate in reactor in which mass ratio of calcium carbonate, ammonium bicarbonate, water, and sodium dodecyl sulfate is 50:69-72:345-355:0.45-0.55, filling container with excess calcium oxide mesh, placing in reactor, stirring at 16-20 degrees C at speed of 900-1100 rpm, tracking reactor solution pH, stopping stirring, removing container filled with calcium oxide mesh, and filtering reactor solution using micro-pore filter to obtain solid which is ultrafine calcium carbonate.    USE - Preparation of ultrafine calcium carbonate (claimed).    ADVANTAGE - Process is simple, short, safe, low cost, and environment-friendly, and has low energy consumption. Ultrafine calcium carbonate has uniform particle size and high purity.    DETAILED DESCRIPTION - An ultrafine calcium carbonate is prepared by stirring calcium carbonate, ammonium bicarbonate, water, and sodium dodecyl sulfate in reactor in which mass ratio of calcium carbonate, ammonium bicarbonate, water, and sodium dodecyl sulfate is 50:69-72:345-355:0.45-0.55, filling container with excess calcium oxide mesh, placing in reactor, stirring at 16-20 degrees C at speed of 900-1100 rpm, tracking reactor solution pH, stopping stirring, removing container filled with calcium oxide mesh, filtering reactor solution using micro-pore filter to obtain solid which is ultrafine calcium carbonate, and filtrate which is ammonium chloride solution, evaporating water in ultrafine calcium carbonate at 105-110 degrees C for 28-32 minutes to obtain product, adjusting pH of ammonium chloride solution to 4.2-4.7 using hydrochloric acid, heating to obtain ammonium chloride solution, stopping heating when crystal film is formed on surface of ammonium chloride, stirring ammonium chloride solution to uniformly disperse film, stopping stirring, cooling to room temperature, filtering, and cooling in which resulting solid is ammonium chloride crystal, and filtrate is saturated ammonium chloride solution.