Abstract: Red clay is characterized by high liquid (plastic) limit, low permeability, medium-low compressibility and highmechanical strength. It is widely used in anti-seepage projects such as roadbed, earth dam, tailings and landfill cover in karst areas of southwest China. The hydraulic parameters of the red clay are tested in laboratory and field. The test area of red clay cover is built in landfill site, and the long-term service hydraulic characteristic parameters are monitored in natural climate. The hydraulic parameters of the red clay cover with and without vegetation are analyzed. The results show that: (1) The saturated permeability coefficient of the red clay is 10^-7 cm/s with low permeability and good anti-seepage performance. The effective water storage rate is about 18.8%, which is equivalent to that of silt and silty clay, and the water storage capacity is acceptable. (2) The large-scale construction in the field and the fine sample preparation in the laboratory lead to significant differences in the structure of the two soil samples. With similar dry density, the saturated permeability coefficient of field red clay is 36.62% higher than that of laboratory remold red clay. The "discount" phenomenon of anti-permeability of compacted soil from laboratory to site should be fully considered. (3) In long-term service of 2.0 years, the permeability of the red clay cover without vegetation increases by the maximum increase of 5×10³ times that at the beginning of construction due to soil cracking under the sun-rainfall cycle. With vegetation, the permeability increases or decreases compared with that at the beginning of construction (the maximum increase of 10 times) and is related to the vegetation growth state. It is shown that the vegetation has an obvious inhibitory effect on the permeability deterioration of fine-grained soil due to sun-rainfall cycles.