Abstract: Through analyzing dynamic deformation testing results of no-clay weak interbed belong to different granulometric composition, we show that damping ration(d) increase along with dynamic strain(d added. Granulometric composition and moisture content will control the damping ration.Testing results show that dynamic effect by earthquake is no evident for no-clay (coarse clastic soil) weak interbed. The dynamic mechanical property of no-clay weak interbed is better than saturated sand soil of raveling and middle density.