Abstract: This approach was mainly concerned with the method for lacaic acid isolation and extraction by salt precipitation after alkaline soluting and impurities removal from raw lac. Factors which influenced the precipitation process were analysed. According to the analysis, a mathematical model for such extraction was set up, therefore the optimal technique conditions were found as follows:NaCl dosage 9.64g, stir rotational speed 800r/min, salt precipitation temperature 34.5℃ and time 25min, alkaline concentration 0.188mol/L. With such optimized treatment, the absorbence value of the diluted precipitating solution reached 0.3508. Another study was carried out based on such solution, aiming to find the precipitation effect on lacaic acid by adding calcium salt. Results showed that the appropriate dosage of CaCl2was 3g/L during calcium salt precipitation treating, and it achieved 95.42% extraction rate 31.28% anthroquinones contents at pH3.633. The DSC and FTIR analysis also implied that impurities contained in lacaic acid products were probably capsulated lac resin from the processing period of calcium salt precipitation.