Abstract: Due to randomness and complexity of seismic action, the instability mechanism of slopes in dynamic analysis is obviously different from that in static analysis. At present, there is no uniform and well-recognized dynamic instability criterion of slopes. In this paper, the plastic strain energy theory and the catastrophe theory are applied to the dynamic stability analysis of a slope, and dynamic safety factor of the slope is determined according to the sudden change of the total plastic strain energy after the earthquake. The dynamic instability analysis of the slope shows that the plastic strain energy criterion is less affected by human factors than the criterion of plastic zone penetration and the criterion of key point displacement mutation. It turns out that the calculation result is more objective and the accuracy of the safety factor is guaranteed. Therefore the proposed method can be a better choice for dynamic instability analysis of slopes.