Because the neutralization lye NaOH used in chlorine absorption system of Baoding Sino French Water Supply Corporation Ltd. after absorbing CO2 in the air could form into plenty of crystal Na2CO3 which blocked the pipe and pump cavity and affected the operation of absorption device, KOH was found to replace NaOH. The experiment results show that KOH has sufficient solubility in low temperature and strong alkali environment , the new formed material still has sufficient solubility after KOH absorbed CO2 in the air, at the same time,still showed in alkaline and has sufficient absorb capability.