Abstract: Trisodium phosphate（TSP） belongs to strong acid-weak base salt,having the strong alkalescence,good solubility and steady chemical property.It can be preserved for a long time.In order to provide the effective trapping of iodine in the water and to prevent the stress corrosion cracking of the metal material,it is necessary to buffer the acid and raise the pH by the addition of trisodium phosphate in the spray water.We have studied TSP application in EAS system through the calculation of TSP quantity,and the ability to adjust pH and dissolution time.The structure and the layout of TSP storage tank could be confirmed.It is concluded that the setting of TSP container beside the containment sump,sodium hydroxide could be replaced by trisodium phosphate.