In order to discover the relationship between the earth surface deformation evolution and the water impoundment/discharge and penetration process in the Longtan Reservoir area, we process a time series of images from Envisat ASAR and ALOS PALSAR instruments using an MT-InSAR technique enhanced by corner reflectors. This allows us to successfully obtain a deformation map from this densely vegetated reservoir area with karst topography. We obtain time series of precise deformation images, which show clearly, for the first time, the complete spatio-temporal earth surface deformation evolution in the whole reservoir area during the impoundment/discharge process. The results from the two kinds of data show a similar underlying pattern: (1) The water load causes subsidence in almost all of its immediate surroundings; (2) the subsidence magnitude shows cyclic variation matching seasonal water level variation. Every year, the water level starts to increase in June and quickly reaches its peak in July to August, and the subsidence immediately follows and also reaches its peak magnitude in July to August; then the water level decreases slowly, and the area rebounds slowly. (3) Statistical analysis of time-series deformation shows that about 60% of the deformation occurs during the rain season (June to August) can be restored, and the remaining 40% become permanent.