During the 1995 Hyogoken-Nambu Earthquake, many important engineering structures were seriously damaged, including soil structures, such as railway embankments and small scale dams. So a new seismic design method of soil structures against large earthquakes was proposed. This is a method for predicting earthquake-induced permanent deformation of earth structures. The method employs a dynamic stress vs. permanent strain relationship of soil, which is determined from laboratory test. This paper describes an outline of the design method and results of calculation.