NOVELTY - Nanometer calcium carbonate, calcium carbide, and fuel gas are prepared by calcining lime stone to obtain calcium oxide and carbon dioxide; dividing carbon dioxide into 2 parts; crushing calcium oxide and passing particles through sieve to divide into 2 parts; introducing first part of carbon dioxide and calcium oxide into furnace filled with wet coke to obtain calcium carbide and fuel gas; adding water and stirring to dissolve some of the particles; stirring slurry, introducing second part of carbon dioxide, and adding crystal formation control agents; and performing solid-liquid separation.    USE - Method for preparing nanometer calcium carbonate, calcium carbide and fuel gas (claimed).    ADVANTAGE - The method reduces crushing process in the production of nanometer calcium carbonate. Carbon dioxide in the preparation process can be recycled in the reactors for preparation of calcium carbide and calcium carbonate, which increases purity of fuel gas products and utilization of raw materials.    DETAILED DESCRIPTION - Preparing nanometer calcium carbonate, calcium carbide and fuel gas involves:    (A) calcining lime stone at high temperature to obtain calcium oxide (CaO) and carbon dioxide (CO2);    (B) dividing CO2 into CO2 (I) and CO2 (II);    (C) crushing CaO to obtain grain diameter of 5-40 mm, and passing particles through sieve with pore diameter of 2-4 mm to divide CaO into 2 parts, in which the part of coarse particles is CaO (I) and the part of thin particles is CaO (II);    (D) introducing CO2 (I) and CaO (I) into reacting furnace filled with wet coke or coal to obtain calcium carbide and fuel gas containing carbon monoxide (CO), hydrogen (H2), and methane (CH4) after a reaction at 900-1600 degrees C;    (E) adding water and stirring to dissolve some of the particles, after the reaction, passing the particles through a sieve to filter the coarse particles, and diluting the filtered slurry with water until calcium hydroxide (Ca(OH)2) is at 5-40 wt.%;    (F) stirring the slurry at 50-500 rpm and introducing CO2 (II) at 5-50 m3/(hour-100 kg Ca(OH)2) for 3-15 minutes of reaction, adding crystal formation control agents in 5-30 minutes; and    (G) performing solid-liquid separation to the obtained product, drying the solid product to obtain nanometer calcium carbonate powder comprising pin-shaped and ball-shaped particles, an average grain diameter of the ball-shaped particles being 30-100 nm and that of the pin-shaped particles being 10-80 nm.    The crystal formation control agents include a first variety of control agent and a second variety of control agent, which are independently added from top and bottom of the reactor at the same time. The first variety of crystal formation control agent comprises soluble aluminum salt (0.1-2 wt.%), while the second variety of crystal formation control agent comprises soluble zinc salt (0.1-2 wt.%).