Abstract: Osman developed a model to describe the riverbank bank collapse based on the slope stability analysis. This model could reflect the physical process of slope collapse well and had been applied to the breach formation model. During the dam break process, the reservoir water level decrease with the increase of outflow, thus transient seepage flow emerge along the slope plane and the seepage force resulting will decrease stability factor of the slope. In this paper, the seepage force was considered to access the stability of bank based on the Osman model. The failure angle and critical value to access the slope stability were calculated. In addition, the breakage process of Teton dam was simulated based on the basic data provided. In addition, the comparison was made between the simulation results when considering the effect of seepage conditions and neglecting it. The results show that the decrease rate of reservoir water level when considering the seepage effect is faster than that neglecting the effect. It takes longer for reservoir to drain off when neglecting the seepage effect. The seepage force accelerated collapse and shorter the dam breakage duration. In addition, the maximum dam break flow rate is greater when considering the seepage effect.