Abstract: Based on the strength reduction FEM, the method for judging the stability state of soil slopes under earthquake action is analyzed. The length ratio of equivalent plastic strain zone in the slope is defined, and the corresponding relationship between the length ratio of equivalent plastic strain zone in the slope under earthquake and the safety factor is established through statistical analysis. Then, according to the corresponding relationship between the stability and safety factor of slopes in the Chinese national standard “Technical code for building slope engineering” (GB50330—2013), the method for judging the stability of the slopes under earthquake by the length ratio of equivalent plastic strain zone is realized. The results show that when the length ratio of equivalent plastic strain zone is 100%, the slope is instable; when it is between 90% and 100%, the slope is understable; when it is between 85% and 90%, the slope is basically stable; and when it is below 85%, the slope is stable. The results may have a great reference value to the rapid evaluation work of seismic hazards of slopes．