In order to study the pore structure evolution behavior of the hardened cement slurry with high-dosage (mass fraction above 20%) limestone powder, based on electrochemical impedance spectroscopy (EIS) and mercury porosimetry (MIP) test analysis, the influence of high-dosage limestone powder on the EIS topological structure and pore structure parameters of the hardened cement slurry were explored. The microstructural equivalent circuit of hardened cement slurry with high-dosage limestone powder was established, and the relationship between components in the equivalent circuit and pore structure parameters was studied. The results show that the effect of limestone powder content on the EIS topological parameters of Bode angle and θmax is significant with the increase of hydration age, and the pore size distribution of the hardened cement slurry with high-dosage limestone powder content is roughly evolved from large pores and capillary pores to transition pores and gel pores. In addition, the resistance of EIS equivalent circuit decreases with the increase of capillary pore content in hardened cement slurry, and the capacitance decreases with the increase of gel pore content in hardened cement slurry.