The behaviors of Daganping clays are obtained under the unloading stress-path by triaxial tests and the goal is to quantify the parameters for stability analysis on slope excavation. A non-linear finite element analysis for stability of slope excavation is established. The results provide a systematic description of the whole process，including deformation behaviors，extension of plastic zone，formation and evolution of slip surface, and failure in slope during excavation. The location of slip surface is determined by the results from the finite element analysis，and the Janbu slice method is used to calculate the safety factors of slope stability. The stability of slope excavation is estimated according to calculating results.