In order to further study the water distribution of expansive soil slope protected by geo-membrane protection scheme during rainfall and evaporation, and verify the feasibility of geo-membrane protection scheme, laboratory model test for geo-membrane protection program is conducted. Make the expansive soil slope model go through the cycle of artificial rainfall and evaporation, in which volumetric water content probes are buried at different depths, so that the moisture content at different depths in the slope model can be measured at any time. The results show that the geo-membrane impede rainwater infiltrating into soil under the geo-membrane during wet and dry cycle, which make the soil under geo-membrane maintain a lower moisture content corresponding with a higher suction in the soil water characteristic curve. This will increase the effective stress of the soil and the stability of the slope. In this paper, to discuss the coverage of the geo-membrane at the back of the slope, the VADOSE/W module in the finite element software GeoStudio is used to simulate an expansive soil subjected to rainfall and evaporation cycle in the natural. By comparing the volume moisture content and suction in slopes of different coverage, it states that when the coverage of geo-membrane at the back of the slope is between 7 and 10 meters, soil under the geo-membrane at the edge of the slope won't be interfered with rainfall and evaporation and maintains a high suction state.