The change of porosity and the tortuosity induced by the swelling progress of Geosynthetic Clay Liner (GCL) influence the hydraulic conductive obviously. The model simulating the seepage in bentonite is established by COMSOL to investigate the effect of the expansion process of bentonite particles on the hydraulic conductive of GCL.The COMSOL simulation results showed that the maximum velocity of the boundary channel is less than that of the non-boundary channel, when the liquid passes through the pores between the bentonite particles, which is consistent with the Poiseuille equation and initially verifies the accuracy of the model. The microscopic particle velocity distri? bution law is consistent with the velocity distribution law of macroscopic fluid field. Therefore, the macroscopic hy? draulic law can be investigated in the microscopic aspect. Meanwhile, the particle expansion on the porosity and the tortuosity of bentonite is analyzed by using the particle trajectory monitoring method in COMSOL. The results showed that the tortuosity decreases with the increase of porosity, and it is exponentially functional. Based on the capillary model of porous media and the Poiseuille Formula, the theoretical prediction model of the hydraulic conductive of GCL, which can reflect the influence of porosity and the tortuosity, is proposed, considering the exponential function relationship between the porosity and the tortuosity. The theoretical calculation prediction model for predicting the hydraulic conductive of GCL is proposed. The ratio of the theoretical and experiments is between 1/5 and 5, which confirms the accuracy of the theoretical model of GCL.