A subsection calculating numerical simulating method is presented, based on the different dynamic responses of rock under blasting and the different limitations of dynamic finite element algorithms and traditional numerical simulating algorithms of seismic wave. The subsection calculating method divides the simulating region into an elastic region in which dynamic finite element algorithms are applied and an inelastic region in which traditional numerical simulating algorithms are applied while displacement is applied to the boundary conditions between different regions. The numerical simulating results indicate that the subsection calculating method is correct and effective in numerical simulations of seismic wave in rock under blasting.