Abstract: This paper analyzes the deformation monitoring data in the creeping rock slope B on the left bank of Longtan Hydropower station by considering the monitoring data of ground water levels and rainfall. The results show that deformation of creeping rock slope occurs above 520 meters in the elevation, and the strong weathering line or creeping rock mass breaking face controls the rock mass deformation of slope B. With drainage and loading at the toe of the slope, deformation velocity of rock mass is gradually reduced and almost reaches a steady state over time. The authors conclude that deformation monitoring near the strong weathering line or creeping rock mass breaking face should be continued, especially during the impoundment period, and therefore surface and ground water drainage systems could thus be well maintained.