Abstract: The aragonite calcium carbonate was synthesized with composite additive MgCl2 and NaOH by gas-liquid carbo- nization method.The morphology and crystal structure of products were characterized by XRD and TEM.The effects of process conditions，such as NaOH addition ratio，Ca（OH）2 concentration，and reaction temperature，on the experimental results were discussed and the reaction mechanism of the process was also analyzed.Results showed that the aragonite in the products was formed by heterogeneous nucleation and growth on the precipitation of Mg（OH）2，and the calcite formed by homogeneous nucleation and growth of calcium carbonate in the solution; the addition of NaOH reduced the supersaturation of calcium car- bonate in the solution，inhibited the homogeneous nucleation process and reduced the adding ratio of MgCl2.The high content of aragonite calcium carbonate can be prepared at the conditions that the initial carbonization temperature of 30 ℃，the con-centration of Ca（OH）2 of 1.7~2.0 mol/L，and the amount-of-substance ratio of NaOH to MgCl2 of 2.6.

Key words: calcium carbonate, aragonite, Ca（OH）2, NaOH