Abstract: In order to explore its micro-mechanism, the time-dependent strength of clay is related to the overlapping mode and interaction potential of plate-like clay particles. The interaction force between the particles causes the particles to overlap toward a position with a lower potential energy. When the potential energy between the particles is the lowest, the time-dependent strength reaches a stable value. A total potential energy formula is proposed to consider the interaction between two adjacent plate-like particles with certain angle θ and distance d, where the Zeta potential can be used instead of surface potential to calculate the potential energy. The calculated results of the total potential energy are consistent with the actual situations. It is shown: (1) The time-dependent strength of clay has a close relationship with the electrolyte content. When the electrolyte concentration is low (≤10^-3 mol/L), the total potential energy is the lowest while the two adjacent particles are perpendicular. When the electrolyte concentration is high (≥10^-1 mol/L), the total potential energy is the lowest while the two adjacent particles are parallel, and the time-dependent strength is almost unchanged, or even reduced. (2) The stable overlap of clay particles is mainly vertical and parallel. The two adjacent particles will always tend to be overlapped each other in one of these two ways, and so it takes some time for clay to reach a stable value of the time-dependent strength. (3) The reason for the restoration of thixotropic strength of general clay may be explained as that particles will always tend to overlap vertically, and this overlap way leads to the highest strength of clay.