Abstract: The dynamic analysis was usually applied to evaluate liquefaction and slope stability of sandy shell and foundation stratum of large earthrock dams against earthquake, the pseudo-static analysis was much widely applied to evaluate seismic slope stability of sandy shell and foundation stratum of medium or small dams. However, not only pseudo-static analysis but also dynamic analysis were accompanied with total stress method up to date. Nevertheless, the total stress method remains some defects, such as, ①the dynamic shearing strength τdf and dynamic internal friction angle φd determined by dynamic tri-axial test were based upon certain failure criteria, while these criteria are quite arbitrary and arguable; ② these parameters were only related to static stress but not related to dynamic response of the dam and foundation; ③ the direction of rupture plane in the testing sample is not consistent with that in dam and foundation. According to these reasons, the accuracy of the analyzed results seems to be doubtful. In order to improve the analyzing method, an effective stress dynamic analysis method for evaluating liquefaction and for slope stability against earthquake is presented in this paper. Besides, the author emphasizes the importance of studying seismic crack of clayey core or apron, and proposes a procedure for studying this problem.