Comparison of the seismic sequences between Tonghai earthquake in 1970 and the Tangshan earthquake in 1976 indicates that the attenuation, number, intensity of aftershocks and shape of epicenter areas were different. In this paper, an interpretation is proposed that aftershocks reflect the adjustment process of the medium in seismic source after severe fracture. If the radio（a/b） from major axis length a and minor axis length b of the aftershock epicenter area is large, it implies the source volume being near to a plane and the adjustment process at the plane should be simple, so the aftershock attenuation is faster and strong aftershocks are less. In opposite case, with small a/b, the source volume is near to a cubic and the adjustment process is more complicated, so the aftershock attenuation is slower and strong aftershocks are more and stronger. It can be attempted to use the parameter a/b to estimate quickly that it the stronger aftershocks will be more or not, and the aftershock attenuation will be slow or not for the case that the aftershocks can be located immediately after the mainshock.