Abstract: Preparation of calcium carbonate from continuous crystallization process of ammonia carbonate and conversion of calcium sulfate was researched. Influences of residence time，crystallization temperature，mass solid-liquid ratio，and stirring speed on conversion of calcium sulphate dihydrate were investigated.Response surface methodology was used to design optimized experiments，a quadratic polynomial regression model for conversion of calcium sulfate and factors was established， and the optimal levels of factors were obtained.Significance of single factors was：residence time>temperature>solid-liquid ratio>stirring rate.Interaction influence of residence time and temperature was significant，and interaction influence of other factors was insignificant.R2 for regression model was 98.17% and P value was significant，and average error between experimental values and predicted values was 0.32%.Optimal level of factors was as follows：residence time was 170 min，temperature was 316.65 K，solid-liquid ratio was 0.050，and stirring speed was 315 r/min.The theoretical conversion of calcium sulfate under optimal conditions was 99.72%， and the experimental value was 99.61%.

Key words: gypsum, calcium carbonate, crystallization, continuous method, response surface methodology