Abstract: The landslide examined in this paper is located in a hydropower station reservoir in Mingjiang River. It is 0.5 km away from dam foundation. The bottom of Baishuizhai older landslide deposit was affected by Diexi Earthquake in 1933 and formed an old landslide (i.e., the examined landslide). The landslide had great deformation after water storage in 2001 at the normal level of 1475 m above sea level. Early in 2003, the water level of reservoir declined to 1470 m and the deformation had slowed down. The terrain and geology conditions were examined and combined with field investigation and analysis of the monitoring data. The increase of core pressure caused by water storage was considered as the major reason of the recovery of this old landslide. A 2D FLAC numerical modeling showed that when the water level changed from 1450m(before water storage)to 1475 m and then to 1470 m, the deformation of landslide had changes of relative smooth to increase dramatically, then to increase slowly down, respectively. Calculation of stability showed that, in the condition of 1475 m water level or earthquake, the coefficient of landslide stability is 0.9~0.99. It means the landslide would occur. In order to make the water level to normal, the landslide needs some remedial measures . The sliding-block with drainage is suggested to be the main method.