The finite element computation for the plant model of containing a group of cracks shows that stress field is homgeneous before the fault slip, but the stress field near the fault changes much large after the fault slip. The direction of the stress field in local area has rotated nearly 90°. It is a possible mechanical mechanism of rotation of P axis in the preearthquake. When the relation of a group of faults in the geology is simulated by the relation of the cracks, the calculation results show that the possibility of slip of some faults is increased, and the possibility of slip of other faults is decreased, because the slip from one of the group of faults. It means that the possibility to occur earthquake is increased for some faults and the one is decreased for other. So, the earthquakes in groups exist the relation under control of the dynamics called the "self-control". Using this result we have divided the "Seismic Curtain" in north China from 1484 to now.