With the uncertainty and complexity of influence factors and the subjectivity and impracticality of traditional methods, a comprehensive evaluation method based on extension theory was studied. The stability of Zhuanghe slope in Liaoning Province was evaluated from the geological conditions, environmental conditions and engineering conditions. At the same time, the level of the slope stability was determined and the factors influencing the slope stability was studied. By calculating the extensible correlation, weight and other indicators of influence factors, the seismic force is the most important index for slope stability. On this basis, the effects of horizontal and vertical seismic force on slope stability were studied from the Coulomb strength theory and the stress state of rock. This method combine the extension theory with the impact of seismic force on slope stability, which not only provides a comprehensive methods for analyzing the slope stability, but also provides a reliable basis for taking targeted reinforcement measures.