Nano calcium carbonate (CaCO3) of good evenness and narrow particle size range were synthesized by controlling conditions and adding agents to improve the evenness and reduce particle surface strength. It was shown that the evenness degree was improved by all additives used, and the particle size was decreased only by additive B. The organic additive A had some influence on the evenness degree and the particle size, but they couldn’t be improved at the same time. The inorganic additive C and D could improve the evenness degree, but couldn’t make the particle size better. The inorganic additive B played a important role in the evenness degree and the particle size, and the nanometer CaCO3 whose size was 19.6nm and the evenness degree was 3.4 could be gained at 0.6 wt.% calcium hydroxide (Ca(OH)2) using B as additive.