Flood discharge atomization is the large-scale rainfall and diffuse phenomenon in local area of downstream during hydraulic engineering flood discharge, which endangers the normal operation of hydraulic structures and stability of downstream bank slope. This paper compares the safety of the flood discharge atomized slope after 13 days’ flood discharge and 7 days’ drainage with 4 and 5 drainage tunnels respectively. The results show that the slope is stable both in the natural and rainstorm condition, and it still stable in the long-term fog and rain condition. Atomized rain infiltration, the slope displacement increase, and the maximum value appeared in the whole slope reached saturation point, and the displacement is reduced after the flood stop. Except for the slope foot, the calculation results of the two drainage tunnel design schemes have little difference, and the addition of a drainage tunnel is beneficial to suppress the water head at the slope foot, which provides the basis for the design of the slope support.