China is an earthquake-prone country，especially in its central and western regions.Earthquake is an unexpected event，and while its occurrence is not frequent，it can be catastrophic，and its effect on high grade highways is no exception.Previous research has rarely addressed the dynamic characteristics of subgrade filing and the stability of subgrade structures under earthquake loads.The effect on the seismic dynamic load，as documented by the current“Code for the Design of Highway Engineering，” typically uses the region of earthquake intensity as its only reference.This code does not consider seismic vibration frequency，the duration of an earthquake，or other characteristics.Therefore it cannot accurately reflect the characteristics of a subgrade structure during an earthquake. In this paper，we carry out research on the dynamic stability of the roadbed structure using the pseudo-static method.We have improved upon the quasi-static method with respect to its formula for the dynamic stability of the roadbed structure.The retaining wall acceleration，as affected by the seismic load，is considered in the calculation of the earth pressure on the retaining wall，as is the influence of the seismic acceleration distribution coefficient.With respect to the roadbed，we also improved the seismic inertia force by introducing the acceleration distribution coefficient.From these pseudo-static method modifications，the stability calculation formula for subgrade slopes was thereby improved.