anshan movement is by far the most important Mesozoic tectonic event in eastern China，this event broke initially stable and intact North China Craton into a series of NE blocks with deep faults, and led to intense igneous activity. Owing to the lack of obvious angular unconformity, there was great difficulty in interpreting the process of Yanshan orogen. Based on the historical research on the concept of Yanshan movement, the stratigraphic comparison between the plain and Western Hills areas of Beijing,combined with the evolution of other late Mesozoic Basin in North China, it is inferred that the time of triggering of Yanshan movement should be after the Middle Jurassic Upper Yaopo coal bearing formation and before syn orogenic conglomerate of Longmen formation. Deep faults caused by the movement formed the tectonic framework of eastern China, and provided channel for intense magmatic activity. According to the extremely brittle characteristics of tectonic deformation (only faulting, no folding), combined with the principles of mechanics of materials, we propose that the Yanshan movement in eastern China is the consequences of very high strain rate, and the deep faulting event, could be defined as the "triggering "of the Yanshan movement, or "the Yanshan event”.