Abstract: It is assumed that the continental crust, such as North China crust behaved as a elastic plate cutted by faults with various trends. Due to the complexity of crustal structure in the course of crustal movement would be formed a lot of stress-concentrated points where are clustered the most precursor phenomena. Some of those points would become sources of future earthquakes. In this paper an attempt is made to explain two kinds of phenomena by concept of multipoints stress field, that is, 1) there exist an isolated precursory-concentrated area long before the earthquake occurrence and 2) the strong earthquakes take place continuously and frequently in a short period, for instance the series of strong earthquakes in North China.