With a lot of experiments on explosion, the dynamic stability of grotto and sprayed anchor strutted grotto were studied under effects of seismic wave of explosion, and a formula was put out for calculating the stability. The results of calculation fitted results of testing well. It is usually needed to evaluated the stability of tunnels and galleries in structures of mines, railroads and hydro-electric engineering under effects of dynamic loading, and the safety distance needed to be determined. The dynamic loads result mainly from explosion work and accidents. When the stability of tunnels and galleries are evaluated under effects of seismic wave of explosion, it should be considered the dynamic loads from explosion as well as static loads from rocky soil. The quantities of dynamic loads are related to amplitude and lasting period of seismic wave of explosion propagated among ground.