The activity of limestone collected from Qingshuihe area in Inner Mongolia was determined and their influencing factors were studied.The results showed that the activity of lime was determined by degree of decomposition influenced by preheating time,preheating temperature and calcining temperature.The optimum technological parameters of determination of lime activity are as follow: the optimum preheating time was 45 min,the optimum preheating temperature was about 800℃,and the optimum calcining temperature was 1100℃.Besides,the lime activity of limestone from Fengshan Formation was better than Majiagou Formation's.Its reason was closely related with high special surface of limestone with loose microcrystalline structure in old strata,which has high reaction area.