Abstract: The similarity in the seismogenic structure, rupture mode and the focal stress field indicates that the earthquake of magnitude 6.0 occurred in Haicheng on May, 18, 1978 can be regarded as a strong aftershock of the 1975 Haicheng earthquake with magnitude 7.3. After main earthquake there have not been intensive activities of aftershocks. But they toke place much later, it may be explained by the disrupture of the locked section of NNE running active structure.The authors of this paper re,fer the strong shocks taken place within 10 years after the main shock to be the late strong aftershocks. By the synthetic analysis of the geotectonic features and the nature of the whole seismic activity series of the Haicheng earthquake, it is shown that the multi-locking structures must be a necessary background and the locations for generating the late strong aftershocks. Its anomalous precursory, however, was less obvious and appeared only along the direction obliquely aerossing the principal structure in area concerned. Some characteristics of the late strong aftershocks and relevant strike-slip mechanism are slao discussed herein.