English：

Composite dams, due to their combination of advantages from multiple dam types, are widelyused under complex topographic and geological conditions. The static and dynamic stability of theirspillway sections is crucial for project safety. This paper takes a composite dam as the research object anduses finite difference software FLAC3D to perform static and dynamic calculation analysis on its No. 12 andNo. 13 spillway sections. The static conditions consider normal water level and dead water level,whilethe dynamic conditions are based on free⁃field boundary conditions and Rayleigh damping,with an inputpeak acceleration of 0.15g artificial synthetic seismic wave （duration 10s）， analyzing dam displacementand stress distribution. Based on relevant national standards and specifications, the analysis results show:Under static conditions, the dam displacement and stress distribution conform to conventional patterns,with the maximum horizontal displacement at the dam crest being 3.43mm, meeting safety requirements;The tensile stress near the hinged beam area is relatively large, suggesting strengthened reinforcement,with no other hazardous areas. Under dynamic conditions, the maximum relative dynamic displacement atthe dam crest is 5.51mm,which is safe and controllable; The tensile stress at the junction of the weircrest and gate pier exceeds the dynamic tensile strength of concrete, and the tensile stress near the hingedbeam is relatively high, requiring strengthened reinforcement,with no other hazardous areas. The studyindicates that the dam structure design generally meets safety requirements, but local high tensile stressareas need optimized reinforcement design.