Abstract: In order to test the hydraulic conductivity function of the Huangtupo No.1 riverside landslide in the Three Gorges Reservoir area, a method for measuring and calculating the permeability of sliding body based on the combination of in-situ seepage test and numerical back analysis was proposed. The drainage velocity and water level data with time was obtained by discharging water with different flow rates from the bottom borehole using flow valve. And the data was then used as boundary conditions and objective functions to numerically invert the Van Genuchten-Mualem model parameters which define the hydraulic conductivity function of the sliding material. The test results showed that the stable groundwater level in the landslide was 4.75 m above the bottom of the borehole, and the recharge rate of the groundwater around the borehole was 0.24 m3/h. The model parameters obtained from the inversion indicated that the sliding material was relatively fragmentized and the grain gradation was not uniform. The saturated overall permeability was 7.54×10-4 cm/s, which was close with the result of borehole injection tests. The permeability coefficient under the unsaturated state was significant influenced by the water content, which was reduced by an order of magnitude when saturation was reduced to 50%.