K2CO3and NH4HCO4 as removing impurity agent,the Ca2 +removing experiment during the process of preparation of KH2PO4 by extracting method was studied. The results showed that,K2CO3 was more suitable for KH2PO4 solution than NH4HCO3 as a removing impurity agent,while hot filtration operation helped separate Ca2 +solution,and improve product performance.