Abstract: In Northern China, the widespread Agro pastoral Zigzag Zone is rather fragile in eco geo environment, and very sensitive and extremely susceptible to disturbance and destruction with an apparent trend to degradation. This is also a region frequented by a variety of eco geo environmental disasters, such as land desertification, climatic disasters, endemic, etc. The mechanism of the formation of the fragile eco geo environment of the zone comprises inner geo dynamical mechanism and outer dynamical mechanism. The former refers to the tectonic movement in the geological history which has laid down the material basis for its specific patterns of land relief and fragile land surface, whereas the latter, the East Asia monsoon and irrational human activities. The joint effect of the two turns the potential fragility of the natural environment into real serious eco geo environmental disasters. 

Key words: agro pastoral zigzag zone, eco geo environment, ecologically vulnerable environment, formation, mechanism, northern China