The traditional theory of electroosmosis interfaces holds that the potential drop at the soil–electrode interface is entirely due to ohmic resistance. However, numerous studies have suggested that this potential drop comprises multiple components. Research on electrolysis has shown that the potential drop at the electrolyte-electrode interface consists of the equilibrium potential and various overpotentials, including ohmic, concentration, and activation overpotentials. Given the electrochemical similarities between electroosmosis and electrolysis interfaces, the potential drop at the electroosmosis interface is likely to involve similar components. To investigate this, the present study introduced linear sweep voltammetry (LSV) to analyze the composition of the potential drop at the electroosmosis interface. Experimental results revealed the presence of an equilibrium potential at the interface of plate-type electrokinetic geosynthetic (EKG) electrodes, accounting for approximately 18% of the total potential drop. The polarization curve associated with the overpotential displayed a distinct linearity, showing that the overpotential at the electroosmosis interface was significantly greater than that observed in the electrolysis control group. This suggests the presence of additional types of overpotentials beyond the ohmic component, particularly concentration and activation overpotentials. Theoretical and experimental analyses confirmed that the prominent concentration overpotential is the primary contributor to the elevated overpotential in electroosmosis systems. Further analysis of the polarization resistance, derived from the polarization curve, reinforced the critical role of concentration overpotential. These findings provide a deeper understanding of the potential drop composition at the soil-electrode interface and offer both theoretical and experimental foundations for incorporating electrochemical considerations into electroosmosis system design. This research presents a new perspective for optimizing interfacial electrochemical performance to enhance electroosmotic efficiency.