Based on the analysis of the response of AC impedance of cement hydration, the mechanism of the hydration process of cement in the initial period was discussed. In this period, the Faradaic impedance in the equivalent circuit is a component of resistance in series with the capacitance. By measuring the double-layer capacitance and the capacitance in Faradaic impedance, the ionic distribution at the surface of the clinker and the electrical properties of the C-S-H gel can be determined.