Abstract: The variation of groundwater levels in a slope is usually used as the major parameter for the monitoring of slope stability. But its influence on the safety factor of a slope is seldom examined. Most indices used in commercial slope stability monitoring devices only show potential dangerous situations based upon experience without any corresponding displacement information. In this study, we use both numerical analysis method and limit equilibrium method to analyze the relationship among groundwater levels, stress, strain, and safety factor of sandy slopes. So, the influence of groundwater water levels on the sandy slope stabilities can be evaluated. It is found in different internal friction angles of sands that the safety factors of the slope will drop down rapidly when the critical water level is approached. This conclusion can be presented with two normalized parameters of FS/tan? and Hw/H. Therefore two rapid assessment charts for evaluating the stability of sandy slopes are established. The method recommended in this study can also be used to evaluate the safety of real slopes which you don’t have detailed influence factors.