Limestone was used as raw materials, Ca(NO3)2 solution was obtained by HNO3 acid hydrolysis and Ca(OH)2 precipitation purification, and food-grade vaterite calcium carbonate was prepared by CO2 carbonization in the ammonia atmosphere. The effects of carbonization process parameters on the regulation of calcium carbonate crystal form were discussed, and the products were characterized by scanning electron microscopy, X-ray powder diffractometer and Fourier transform infrared spectroscopy. The mechanism of NH+4 and NH2COO- co-regulating the formation of vaterite crystal form was proposed. The results show that the ammonia atmosphere is helpful to the stable nucleation of vaterite-type calcium carbonate. When the concentration of NH3·H2O is 13% (mass fraction), the flow rate of CO2 is 0.5 L/min, the reaction temperature is 25 ℃, and the reaction time is 25 min, the single phase vaterite calcium carbonate microspheres of 2~5 μm are prepared. The purity of the product is 99.5% (mass fraction), and the quality meets the requirements of food safety national standard food additive calcium carbonate. The research provides a theoretical basis for the high-value utilization of limestone and the preparation of metastable vaterite calcium carbonate.