Abstract: In the layered soils, the common Lucas-Washburn (LW) model that describes water movement in homogeneous soil always loses effectiveness under the influence of interfaces between adjacent layers. To characterize vertical water rise under capillary force, a laboratory model test was performed, in which soil moisture content profiles were monitored using the actively heated fiber optic method (AHFO). Based on the results obtained using the AHFO method, the LW model was revised, and an improved LW model (ILW) model was proposed. The experimental results show that (1) when the capillary water wetting front arrives at a “lower clay-upper sand interface”, a “capillary barrier ” can obviously be observed, which makes the soil moisture content above the interface much less than that in the lower soil; (2) the “capillary barrier effect” is caused by the unbalanced matrix suction between sand and clay; (3) while the capillary water wetting front reaches a “lower sand-upper clay” interface, the “anti-capillary barrier effect” around the middle interface appears, which leads to the soil moisture of the upper clay much larger than that of the lower sand; (4) the LW model becomes inaccurate due to the impacts of the “capillary barrier action” and “anti-capillary barrier action”, and (5) compared with the LW model, the ILW model has higher accuracy in the layered soils.