Abstract: The instability of expansive soil slope is vital to the security of water supply in the Middle Route project of South-to-North Water Diversion. Anti-seepage control is considered as an effective method to deal with the instability problem of expansive soil slope. Based on the weak ecological function and short life of the traditional methods to deal with the drainage-seepage phenomenon of slopes, the unsaturated drainage structures are introduced to control rainfall to infiltrate into slope soil. Then two unsaturated drainage structures, i.e., fine/coarse grain soil layers (dual-structure) and coarse layer (single-structure) are chosen. The anti-seepage effects of the both structures on the slope in five rainfall tests are investigated. The results show that: (1) The dual-structure can effectively prevent rainfall from infiltrating into the slope, without leakage at the bottom of the expansive soil in the experiment with rainfall intensity of 4.18×10^-4 cm/s. When the initial soil water content of the fine grain layer is lower with a strong storage capacity, the anti-seepage effect is better. (2) The single-structure can protect the expansive soil slope at a certain extent, with the rainfall intensity of 1.72×10^-4, 4.18×10^-4 and 4.97×10^-4 cm/s, however, 5.6%~10.7% of the total rainfall flows out at the bottom of the expansive soil, which indicates the single-structure leakage risk. In a word, the anti-seepage effects of the dual-structure on the slope are better than those of the single-structure. This study is helpful to dealing with the expansive soil slope in the Middle Route project of South-to-North Water Diversion.