It is important to utilize marine sand as raw materials in civil engineering. The influence of the marine sand to the properties of cement and steel materials are concerned. In this paper, the electrochemical impedance spectroscopy(EIS) method is introduced to study the hydration behavior of the mortar with marine sand, in order to make an interpretation of the function of marine sand on the cement materials. The results of experiments show that the hydration of mortar with marine sand is a complex procedure and it holds both dielectric characteristic(low frequency in EIS) and electrolytic characteristic(high frequency in EIS). The releasing of Cl- is a continuous procedure and it is long term acceleration for hydration of mortar. The more concentration of Cl-, the more contents of hydration product Ca(OH)2 is produced from the surface of C S H gels. It will make the proportion C S H gels decreasing, whereas the proportion of Ca(OH)2 and ettringite increasing.