Abstract: 【Objective】Soil slope is easy to form cracks under the rainfall-evaporation cycle, which leads to rainfall infiltration into soil and induces slope instability. Based on ecological priority, this paper proposes a fine / coarse unsaturated capillary barrier layer ( CBL ) with ecological function to inhibit rainfall infiltration slope protection method. 【Methods】Physical model tests were carried out to study the influence of CBL on rainfall infiltration with different rainfall intensities ( 1.93×10-4cm/s, 4.73×10-4 cm/s ) and different CBL lithologic structure compositions ( sub-sandy soil/coarse sand, sub-sandy soil/gravel sand, sub-sandy soil/breccia, sub-sandy soil/gravel ). 【Results and Conclusion】The main conclusions are as follows : (1) The soil water flows mainly as vertical uniform pattern in the fine-grained layer, while the flow velocity increases with larger grain diameter of the coarse-grained layer, which is obviously affected by the particle morphology of the coarse-grained layer. The soil water flows into the fine / coarse interface of the CBL, which flows along the interface to the toe of the slope. After the soil water breaks through the fine / coarse interface of the CBL, soil water flows in the form of preferential flow and the degree of preferential flow increases with the larger coarse particle size. (2) The stable drainage efficiency of CBL ( the ratio of stable drainage intensity to rainfall intensity ) decreased with the increase of rainfall intensity, and the extent of increase is larger with higher rainfall intensity. The comprehensive barrier efficiency of CBL ( the ratio of total lateral drainage to total rainfall ) increase with both larger coarse-grained layer particle size and higher rainfall intensity, though its growth rate diminishes at higher intensities. (3) Sub-sand/breccia CBL has the best effect on restraining rainfall infiltrating into slope. The research results might provide important reference for the slope stability treatment.