Abstract: The Jin'anqiao Reservoir located in the middle Jinsha River, has suffered different levels of landslide on the bank slopes since its impoundment in 2012, and variation in its seepage field is one of the main causes for such geo-hazards. In this study, we developed a two-dimensional saturated-unsaturated seepage model for gravel soil slopes in the impoundment region according to the engineering investigation, and simulated the evolution of seepage flow and the corresponding slope stability for the stages of initial filling, normal operation and drawdown, focusing the analysis on the influences of water level fluctuations and drawdown rate on saturation line and slope safety factor. Results show that at initial filling stage, the saturation line presents downward convex and the safety factor is increasing monotonically; in normal operation, the saturation line tends to vary gradually and the safety factor is decreasing monotonically and gradually; in drawdown period, the saturation line is upward convex and the safety factor is decreasing monotonically at a higher rate. The slope in the investigation area is an accumulation of ancient landslides, and hence it shows an unstable feature of slope safety coefficients less than 1.0 at all the three stages. This provides an evidence for high potential landslide in this region. The drawdown rate is inversely correlated with slope stability.