Under the guide of Cross high resolution sequence stratigraphy theory, based on areal geology, sedimentary facies, well logging, well drilling and core data in Xiasiwan area, the multistage cyclic sequence division scheme and electrofacies analysis technology are adopted to divide the eighth member of Yanchang Formation intomid-term, shortterm and super-short-term base level cyclic sequences. Every base level cyclic sequence can be subdivided into asymmetric upward-deepening, asymmetric upward-shallowing and symmetric base level cycles. The depositional setting，superposition style and sedimentary dynamics process of the super-short-term base level cyclic sequence are emphatically discussed. Isochronous stratigraphic framework of the eighth member of Yanchang Formation is established by making the short-term base level cycle as isochronous stratigraphic unit. This study provides geologic foundation for the cognition of sand body distribution lawand the planning of exploration and development scheme.