Dynamic crack propagation analysis was used to assess the seismic safety of concrete gravity dams in large-scale earthquakes. Since damping characteristics have been shown to have a major effect on the occurrence and propagation of cracks in dam body, we first discuss damping characteristics by comparing existing shaking table test results with the results of dynamic crack propagation analysis. We then perform dynamic crack propagation analysis on a full-scale dam model to make clear crack occurrence and propagation during a large-scale earthquake. By performing dynamic crack propagation analysis while varying the acceleration level of the input seismic motion, we define the residual factor of ligament length as a new measure related to the crack propagation length, and we use it to perform a quantitative evaluation of seismic safety against crack penetration failure