Abstract: The height of Sanbanxi face-slab rock-fill dam is 185.5 m．With low storage water level, the seepage was less than 30 L/s．As water level rising rapidly in the flood season of 2007, the seepage increased, whose maximum was 303.10 L/ s.By underwater inspection, damage was found at the horizontal joints of the face－slab.Later, rehabilitation was carried out and good effect was gotten.This paper, combined with seepage monitoring data, analysed the seepage of the dam before and after the rehabilitation.