Abstract: According to the quantitative formula of aquifer stress and water level of wells based on 1D half-space horizontal layer model, the present tectonic stress field of Pan-North China region is studied using observational water level data in about 40 wells of ground water observation network of China Seismological Bureau. It is assumed that ascending water level means compression enhances and extension weakens of stress field; descending water level means extension enhances and compression weakens of stress field. Our water level data suggest that the well water level, distributing along Zhangjiakou-bohai tectonic belt and Shanxi tectonic belt, shows ascending and earthquakes with M≥5.0 occurs more frequently at the same time during 1995~1998, which means the compressional stress field enhances, while the water level shows descending and no earthquake with M≥5.0 occurs in whole North China region since 1999, which means the extensional stress field enhances. The result mentioned above may province the background information regarding present tectonic stress field of North China region for earthquake predication research.

Key words: Water level in deep wells, Present tectonic stress field, Seismicity, Pan-North China region