Abstract: Based on the pseudo-static equilibrium of infinite slope and the earthquake-induced pore water pressure of saturated loess,the effects of earthquake-induced pore water pressure on seismic and post seismic stability of saturated loess slopes were investigated.In loess slopes the shear strength reduction caused by pore water pressure might lead the slope to a permanent deformation,to a slide failure or to a flow failure if liquefaction condition were approached.A threshold value of the cohesion of loess was introduced to distinguish the eventual failure modes,and two threshold values of the earthquake induced pore pressure ratio were given to evaluate the effect of shear strength reduction on the slope failure mechanism.The results were presented in the form of stability charts and a procedure for the evaluation of the seismic stability condition was described.