Abstract: Mechanical phenomena of the precursors and aftereffect of large earthquakes can be induced to the interaction of the regional stress field and sourc es.Studing freedback action of sources on the field might be important to propose the model for the precursors and aftereffect of earthquakes in large scale.#br#Based on the seismicity and observation data before and after great earthquakes, the facts and features of influence of sources on the field have been summerized.According to calculated results of the non-linear finite element method, the range and main features of the influence have been obtained.Some of precursors and aftereffect phenomena in recent three large earthquakes occurred in North China have been preliminaryly interpreted.