Abstract: The capillary barrier effect is a natural phenomenon during the infiltration of unsaturated soil layers with different particle sizes. In order to test the capillary barrier effect of multi-layer soils, laboratory model tests are designed. Subsequently, the actively heated fiber optic (AHFO) method is used to test the water migration of the model tests, and the direct observation method and the frequency domain reflection (FDR) technology are used for verification. The analysis of test shows that compared with the direct observation method and the FDR method, the AHFO method has a better observation effect on the capillary barrier phenomenon caused by rainfall infiltration, and can observe more details of water movement as well. The FDR method is used to perform the in-situ calibration of the AHFO sensor, and the curve-fitting accuracy R² is greater than 0.93, indicating a high accuracy of volume water content monitoring. The capillary barrier layer has a significant retarding effect on rainfall infiltration, that is, infiltration water can be saved at the storage barrier which can also reduce seepage to the layer under the barrier. The research results may provide a new method for the research on capillary barrier effect and the monitoring of water content distribution.