The synthesis rate of calcium hydroaluminosulfate, which has important effect on desulfurization and desilicon in alumina production, has been studied. On the basis of the analysis of the two-level multi factor test, the reaction temperature, reaction time (min), Na2SO4 concentration in solution and total alkali concentration, the significant factors affecting the synthesis of calcium hydroaluminosulfate have been screened out. Taking the significant factors as the study object, and by the central composite experimental design and response surface analysis to simulate the synthesis process, a prediction model of the synthesis rate has been got. The technological conditions are obtained by optimization as that: reaction temperature 75℃, reaction time 65min, Na2SO4 concentration in solution 40g/L and total alkali concentration 45g/L. Under this condition experiment, synthesis rate of calcium hydroaluminosulfate obtained was 69.72%, with the small difference from model prediction value 70.24%.