Soil hydraulic conductivity depends not only on the state variables such as void ratio and pore size distribution, but also on its physical/geotechnical properties. In this study, Atterberg limits, hydraulic conductivity and mercury intrusion porosimetry (MIP) tests were performed on MX80 bentonite/Callovo-Oxfordian (COx) claystone mixtures. Based on the experimental results obtained in this study together with the test data compiled from literature, a general capillary model considering Np pores in series was used to evaluate the influence of soil plasticity on the relationship between hydraulic conductivity and pore size distribution. It was found that the best pore interconnection parameter Np was highly dependent on the soil property. The larger the plasticity index, the larger the best Np value and the more complex the pore interconnection. The relationship between the best Np value and plasticity index could be well described by an exponential equation. The general capillary model was then improved to estimate the hydraulic conductivity of different soils. The estimated values using the improved general capillary model were finally compared with the measured ones and the good agreement between the measurement and estimation revealed the good performance of the proposed model.