Under the combined action of heavy rainfall and earthquake, ignoring the spatial distribution characteristics of the geodynamic parameters of the slope, and using the safety factor of the potential sliding surface as the evaluation index will inaccurately assess the stability. The Shiliushubao old landslide in the Three Gorges Reservoir area is taken as the research object. Under the combined action of rainfall and reservoir water level change, the slope remains stable, but lacks seismically evaluation. To accurately analyze the seismic stability of old landslide, the artificial seismic wave model is used. By studying the spatial distribution characteristics of Cyclic Stress Ratio (CSR) of the slope soil, the dynamic parameters of the slope soil were adjusted. Based on the Newmark sliding displacement method, the permanent displacement of the reservoir bank slope was optimized. Firstly, based on the equivalent linear analysis theory, combined with the dynamic triaxial shear test of cyclic load, the variation of excess pore water pressure and dynamic shear modulus of slope soil will be obtained under the different CSR conditions. Then, considering the characteristics of frequent earthquakes in the Three Gorges reservoir area, the stochastic ground motion model is adopted which generates the artificially seismic wave for the Shiliushubao old landslide. Finally, the QUAKE/W module of GeoStudio 2018 is used to calculate the random ground motion and the dynamic parameters of the slope is obtained by the spatial distribution of CSR. The seismic stability of the reservoir bank slope is evaluated by calculating the permanent displacement. The conclusion shows that the shallow colluvial silty clay of the Shiliushubao old landslide is not prone to liquefaction. And under the heavy rainfall and the most unfavorable reservoir water level change, if the fortified earthquake is encountered in the reservoir area, the permanent displacement of the reservoir bank slope is less than the critical permanent displacement, which indicates that the Shiliushubao old landslide will not slide again.