In this paper the space-time-intensity distributional pattern of the moderate and small earthquakes before the strong earthquake occurred du-ring the peak period of the fourth active stage in North China is analysed It is found that the regional seismicity before each strong earthquake occ-urence with magnitude m≥7 undergoes a similar variation which is called the developmental porcess at various stages of strong earthquake.The peak period of seismicity in North China consists of such developmental proce-sses.On the basis of the similar pattern of seismicity and characterist-ics of related energy ratio in such processes,the developmental process of strong earthquake in North China can be divided into three different peri-ods:
period A-the preporative period;
period B-the severe Period;
Period C-the immediolely Period.
The characteristics and some regularies of the seismicity during these Periods show the stress and strain variation of the ground medium in North Chinn and coincide with the present concepts about the fracture mechanism.T-herefore it is considered that the development of strong earthquake is d-ependent on the action of the regional stress and is related closely to the active variation and progress of regional moderate and small earthquak-es.A simple model of the earthquake development——the stop-Pass model——is proposed·The research of the characteristics of seismicity and divis-ional indications by stages in the developmental precess of earthquakes in North China may give a clue to predict the strong earthquakes in this re-gion