Calcium leaching is a degradation progress inside hardened cement composites, where Ca²⁺ ions in cement pore solution can migrate into the aggressive solution. In this work, calcium leaching of graphene oxide (GO) reinforced cement composites was effectively characterized by combined techniques of electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). Inhibiting mechanism of GO on calcium leaching of the composites was also examined. The obtained results show that the diameter of the semi-circle of the Nyquist curves of leached samples with GO addition decreased less than that of controlled samples. After leaching for 35 days, loss rate of model impedance R_CCP of leached samples with 0, 0.05, 0.1, 0.15, and 0.2 wt.% GO addition was 94.85%, 84.07%, 79.66%, 75.34%, and 68.75%, respectively. Therefore, GO addition can significantly mitigate calcium leaching of cement composites, since it can absorb Ca²⁺ ions in cement pore solution, as well as improve the microstructure of the composites. In addition, coupling leaching depth and compressive strength loss were accurately predicted by using the impedance R_CCP.