Abstract: Taocha-Shahe main canal, which is a fully excavated canal of Phase I of Middle Route Project of South-to-North Water Diversion, has a high slope and high-level groundwater. The effect of drainage system in the slope is vital to the safety of the slope and concrete linings. The seepage fields under different conditions are simulated by means of the finite element method associated with drainage designs of the slope. It follows from comparison of the simulated results that the influences on the seepage fields may be neglected while the distance from the boundary of groundwater to the slope is over 600 meters and the altitude of bottom boundary is lower than 75 meters. The sand filter layer under the concrete linings plays an important role in the drainage effects, or there should be 5 layers of drainage pipes to maintain the drainage effects if no sand filter layer exists. The research results provide important references for the design of the slope drainage system.