Some simplified hypocenter models are presented for explaining an im-portant effect of environmental stiffness,which includes the axial and the lateral stiffness and that of fault zone tips,on shock generation pro-cess of hypocenter.Besides the strength condition,the environmental stif-fness condition is another one necessary for shock-generation.The effect of environmental stiffness may reduce the magnitude of mean stress drop in hypocenter to the order of 10² or even 10 Mpa,and the lower stress drop may occur at higher confining pressure.Some problems are discuss-ed:two different kinds of locking segments on fault zone-the potential “seismic core”and the“tip”which constrains shock-generasion;two pos-sible effects of water injecting into different parts of hypocenter region- inducing or preventing strong earthquake;the relation between the geome-tric parameters of environmental stiffness and the distribution of seismic intensity.