In the activity of a seismic sequence, there is often a destructive earthquake after the swarm.It is difficult to say that they belong to the same sequence, but it is possible that they are related each other in mechanism.In this paper, we discuss it from the energy idea. It shows that the volume and the area of the aftershock are related to the energy of the major earthquake.when the released energy is only a little part of the strain energy, then the remained energy is corresponding to the forthcoming strong earthquake.