Abstract: Based on distribution characteristics of anomalies of underground fluids and gravity in the North China,the features of deep-seated material and stress field in the shallow crust before and after main earthquakes are discussed combining the geophysical prospecting data.The water level anomalies close to the epicenter of the strong earthquakes belong to the decreasing-type,but the gas anomalies are the increasing-type before the main shocks in the continental rift valley of eastern China and Shanxi graben system.The water level anomalies far away from the epicenter,however,are usually the increasing-type.There are the orientation trends of the increasing-type and decreasing-type of anomalies of water level before Haicheng and Datong earthquakes.Deep-seated material （especially fluids） rises during earthquake generation in the epicentral area, which results in expansion of the shallow crust,subsidence of water level and gas escape from strata.The stress field of the shallow crust in the epicentral area seems to be expansive with the action of upward stress,but compressive far away the epicenter.The stress field in the shallow crust was the compression-shearing type in the epicentral area of Haicheng and Datong earthquakes.The distribution characteristics of seismic precursors can reflect the state of stress field of the shallow crust in the certain tectonic region and have a close relation with the seated material movement.

Key words: Seismic precursor, Anomaly distribution, Deep-seated fluid