The Dayantang landslide lies at the dam’s back side of Shuibuya Hydraulic Power Project on Qing River, and it is in the center area of strong atomized rain caused by flood discharging of the spillway. For atomized rain influences groundwater distribution of the landslide obviously, the stability of the landslide is unoptimistic. For entire understanding the distribution of underground water flow field inside the landside body under different outside infiltration conditions, the authors simulated groundwater table of the landslide under natural rain and high atomized rain with three-dimensional unsaturation stable seepage finite element method, and mostly compared the seepage control effects of different anti-seepage measures. The calculated results show that the landslide body will be lain in wholly saturated status under the action of the lasting atomized rain. Setting a anti-seepage drain works can effectively decline the underground water level inside the landslide body, and even if cracks occur on the surface of the anti-seepage system, the underground water level inside the landslide body will basically be controlled in a lower water level with a better underground drain system.