Abstract: Under the guidance of principles and analytic methods of high-resolution sequence stratigraphy,and through an o- verall analysis on drilling and logging data,identified are the long-term stratigraphie base level circle(the 3rd sequence) LSC1 and the corresponding 4 middle-term stratigraphic base level circles(the 4th sequence)as MSC1,MSC2, MSC3 and MSCA in the lower segment of Ganchaigou For- mation at W unan area,Caidam basin.Two types of deposi- tional systems--namely braided river delta and lake depo- sitional ones are analyzed,and within the correlation frame- work,the eomposition of the depositional system and the fa- cies development in the cycles are studied.Analytie results show that the increasing half-cycles MSC2 and MSCS are the most favorable reservoirs,and the area in the east- north of the well Wu 8 at the edge of delta is the most favor- able regions for searehing petroleum.