Atomization is serious during the high dam flood discharges. Different flood discharge and energy dissipation modes have different degrees of atomization. Atomization rain causes strong erosion on the slope surface near the dam，and in some slope infiltration，it often causes deep sliding slope disaster. A deposit of a power station downstream was selected to establish unsteady seepage calculation model， and different conditions for numerical simulation were developed to study the changes of expansion process of transient saturated areas and changes of safety coefficient and the relationship. The results show that the influence of different atomization rainfall intensity on water infiltration slope were different， and the greater intensity of atomization rain led to greater transient saturation area and the smaller stability and safety factor of slope，where the safety-factor was reduced to at most 6.57%.