Recently, widespread thick ranging from 10 to even 100 meters loose accumulations were found below modern rivers bed during China's hydropower resources development process. Deep overburden on river bed not only seriously hampers the dam site selection, impacts correlation basin hydropower resources development and exploit, but also brings enormous difficulties to dam engineering design. Because deep overburden is buried under modern river bed and its formation ages priors to the first and second terrace, this phenomenon is contrary to common sense of the river evolution, so its causes have been confused. Deeply cut valley and deep accumulation events, global climate change, sea-level eustacy motion and crustal movement organically linked up are reported for the first time in this paper. The author points out a new viewpoint that global sea level greatly change during ice age and interglacial stage is the main reason that causes deep river valley and forms deep accumulation. On this basis, this paper explain that global climate change result in sea level and erosion basis considerable growth, and causes and processing of production deeply cut valley and deep accumulation by applying the principle of sequence stratigraphy. Finally, this article further related large ancient landslides preparation and occurence along river and deeply cut valley events. The author propose a new perspective that along river large ancient landslides were formed by front free face better in the deeply cut valley period. Therefore, these new views provided a reasonable explanation on the elevation of landslide front shear opening below the modern river bed over 10 meters.