Abstract:In the reliability analysis of a slope,by using finite element method(FEM),which only considers the property of elasto plasticity or material nonlinearity. However,it exists the locally large strain in most soil slopes. It has been proven by experiments that the local strain can reach the value of 40% while the average strain is only 10%. Therefore,it¢s necessary to carry out large deformation finite element analysis of a slope in order to simulating its real failure property. In this paper,the constitutive relationship of the soil is considered as realistic elasto plasticity one and the Mohr-Coulomb yield criteria is adopted. Based on the basic principal of nonlinear continuum mechanics,a kind of elasto plastical large deformation finite element analysis model is built by using updated Lagrangian method,which can consider both the nonlinearity of material and geometry. Then,the method of strength reduction is adopted to calculate the factor of safety (Fs) of a slope. Among the several methods of reliability analysis such as mean first order second moment method (MFORM),advanced first order second moment method (AFORM) and Monte Carlo simulation method (MCSM),the AFORM is used in this paper since it is the most popular method. Through the comparative calculations of factor of safety and reliability index( ) by FEM of small and large deformation and the sensitivity analysis of parameters,the conclusion is that when the large deformation property is considered,the value of Fs will arise while the value of will drop. The reason is that the value of Fs is more sensitive to the value of cohesive c in this situation. Therefore,the limit state function Z has larger variation and smaller reliability index. From this point,it¢s unsafe if the large deformation property in the finite element reliability analysis of a slope is not considered.