Sodium pyrophosphate that melting point is $79-80^{circ}C$ have been Studied on heat storage and heat discharge. In heat storage process, sodium pyrophosphate was kept up initial temperature $50^{circ}C,;60^{circ}C,;70^{circ}C$ which melt by heated water at temperature $85^{circ}C,;90^{circ}C,;95^{circ}C$. In heat discharge process, initial temperature of sodium pyrophosphate was maintained at temperature $85^{circ}C,;90^{circ}C,;95^{circ}C$ which varied cooling temperature $50^{circ}C,;60^{circ}C,;70^{circ}C$. The experiment has been reached conclusions as follows. 1) Heat transfer properties of phase change material is controlled by conduction during heating and cooling process. 2) The temperature increased rapidly at initial stage and transient region increase slowly because of characteristic of latent heat. 3) The lower cooling water temperature is the less the time that get to thermal equivalent state take during discharge process. 4) The higher cooling water temperature is the less temperature difference between top and bottom in P.C.M during discharge process.