Abstract: Based on assumption of the pore water level is horizontal line and no seepage occurred in the slope, the influence of water-level fluctuation on stability of slope is presented through limit equilibrium method. It is shown that the factor of safety (FO8) of slope changes from slow decrease to rapid increase with water level slow raise, which get minimum value when ratio of water level-height of slope at 0.3, on the contrary, which get maximal value when water level as height as slope. There is no influence on FOS when the water level higher than slope. Further more, the FOS became less at water level rapid drawdown or rapid raise up than slow fluctuation. In order to avoid failure of slope, it is advised that water level fluctuated as slowly as human could controlled.