With the most advanced theories in seismic stratigraphy and modern sedimentology sevensedimentary facies and four major depositional systems，-such as river—delta-axial turbidity currentdepositional system，may be distinguished in the study area． In the Shenxian hollow，the quality of seismic profiles is poor，the volcanic activities are veryfrequent，the sedimentary facies change is rapid，and the structural movement is rather strong．Sothe construction of seismic reflection models is the key to the studies of sequenece stratigraphy，sedimentary facies and structure． There are four factors that determine the development and distribution of the depositionalsystems in the area；they are：structural movement，lake—level fluctuation，paleoclimate and sourcearea．of which the first factor iS the most important．