As the oilfield development entered the middle and late stage，difficulty of tapping residual oil increases when the relationship between oil and water becomes more and more complex. Fine geological research based on reservoir architecture becomes the key to tap residual oil. The hierarchy interface analytical method was applied in the article to analyze the internal architecture characteristics of sandy braided-river in the 4th area of L Oilfield in Bohai Bay Basin based on outcrop，core，modern deposits and dense well logging data. On the basis of architecture reverse classification scheme，the architecture interface of braided-river in the study area was divided into 6-12 levels considering positive sequence classification. Based on the experience formula for sandy braided-river reservoir，modern deposits constraints and stratigraphic correlation between closely spaced wells，single braided channel belt，braided bar and braided channels and interlayers within braided bar were quantitatively characterized by grade. A set of methods for quantitatively characterizing different levels of sandy braided-river were developed，and the characteristics of single braided channel belt，braided bar and braided channels and interlayers within braided bar were determined as the three levels of the architecture. There are four filling patterns for the braided channels，including sand filling，half-mud filling，mud filling and remaining mud filling，and then the genesis of different filling patterns was analyzed.