Abstract: The shear strength reduction is combined with fast lagrangian analysis of continuum method(FLAC)to analyze the stability of soil slope, and the FLAC software post-processing ruction to dynamic demonstrate is used in generalizing shear strain increment,plastic areas occurrence and development situation. Moreover, convergence of statics equilibrium algorithm, mutation of displacement on characteristic position of slope as well as continuum of shear strain increment are used as cri- terion to estimate the stability of slope. The critical slip surface can be obtained when the slope become unstable. The method can vividly forecast the latent critical slip surface and evaluate the stability of soil slope by analyzing the international calculated example.