Abstract: The induced crystallization reaction in a CaCl₂-Na₂CO₃ solution system will be initiated under the precondition that the concentrations of Ca²⁺ and CO₃^2- are in the metastable region.A critical value is the boundary point of the metastable region,which was investigated in this study by the electric conductivity method.Various factors that influence the critical value,such as temperature,pH,reaction time and agitating strength,were investigated,and graphs of the metastable region of the CaCl₂-Na₂CO₃ solution system were drawn under various conditions.The results showed that lower temperature,higher pH and proper agitating strength are favorable for decreasing the electric conductivity when the critical value appeared in the solution,or to expand the metastable region.Taking maneuverability and cost into consideration,the optimal reaction conditions for induced crystallization of the CaCl₂-Na₂CO₃ solution system were: temperature 25 ℃,pH 9.0,agitating time 10 min and agitating strength 200 r/min.Under such conditions,the induced crystallization reaction was guaranteed to proceed in the metastable region if the relation between the concentration of Ca²⁺ and CO₃^2- was satisfied according to 3.496×10^-10［Ca²⁺］^{-1.182 6} < ［ CO₃^2-］ < 4.96×10^-9［Ca2+］^>/sup>-1.