Abstract: The Haicheng Earthquake of May 18, 1978 occurred in a Gap of the aftershock area of the Strong Haicheng Earthquake of magnitude 7.3 of February 4, 1975.The monthly rate of attenuation of the aftershocks (Ms2.0) was abnormally Iow(p = 0.73). However, after the earthquake of May 18, 1978, the value of p obviously increased. That is to say, it occurred at the inflection point of the attenuation curve of the monthly rate of aftershocks.Contrarily to the mainshock of magnitude 7.3, before this earthquake, not much fore-shock activity appeared. It constitutes the strongest aftershock of the mainshock. The author believes that it is an aftershock caused by the concentrated accumulation of tectonic regional stress within the unbroken gap area.