Abstract: In order to study the effect of ground water on high and steep open pit slopes, FLAC^3D was employed to simulate and analyze the stability of a high and steep open pit slope. The comparison was made on the effect of the stress, failure zone and displacement in the slope under the condition of ground water or not. The result indicated that ground water reduces the stability of the high and steep open pit slope. A new method for stability assessment of the slope was proposed so as to give rise to reliability of the numerical simulation, which estimated the stability of the slope through the comprehensive analysis of the movement trend of velocity at the tracing points in the model, the failure zone as well as the displacement.