Abstract: To identify the sedimentary characteristic and divide the sedimentary type of Chang 4+5 and Chang 3 Member of Yanchang Formation midsection of Baibao area in the Ordos Basin,the main me-hods used include the core observation,well logging data analyses and description of deposition system and sedimentary facies.It is found that the deposition system is lacustrine-delta in which the delta front develop in the northeast of the studying region and the shallow-lake deposits develop in southwest which scale is small.The shallow water platform delta is develop chiefly in region of studying and the completion prograded sequence is absent.Owing to the subaquatic distributary channels diversion,the sand of subaquatic distributary channels and the mudstone of interchannel are intimate associated and repeated overriding or the sand of subaquatic distributary channels is located on the mudstone of lacustrine facies directly in individual well section.