In view of the shortcomings of the equal-diameter capillary bundle model，this paper theoretically derives the multi-segment imbibition formula of the variable-diameter capillary under the liquid-liquid system considering pressure difference and solidliquid wall effect by using the sectioning method. In addition，the paper studies the influence of changes in different capillary geometry and fluid properties on the imbibition-displacement of the variable-diameter capillaries and develops a random variable-diameter capillary bundle model through Python，so as to deduce calculation methods of the recovery and water cut based on this model. The results show that the increase in pressure differences leads to the decrease in the differences of the imbibition velocities between variable-diameter capillary segments，and the imbibition-displacement of the variable-diameter capillaries is directional. The recovery and water cut calculated based on the random variable-diameter capillary bundle model are in good agreement with the real core displacement data from experiments，and the contribution of the imbibition effects to the total recovery reaches 19.97%.