Abstract: To study the inner architecture and remaining oil distribution in the mouth bar of meandering river delta, based on the production performance and core data in the Wellblock Cai-10 and Caican-2 of Cainan oilfield, the paper performs detailed analysis on the mouth bar architecture by using the methods of analytical hierarchy process, multi-dimensional interaction and dynamic verification, and establishes mouth bar architecture models for the meandering river delta in the study area. The study shows that there are 2 categories of marks to identify single mouth bar boundary, namely vertical superposition of the units of different periods and lateral merging of the units of same periods, among which the latter structure can be classified into 3 types such as main body—main body of the mouth bar, main body—bar margin—main body and main body—between-bar mud. There are 2 mouth bar architecture models such as progradation and accretion. The progradational architecture model mainly refers to the structures in which the sediments of late stage accreted and superposed onto the mouth bars of early stage when the distributary channel was under the circumstance of stable hydrodynamic force, and the lateral accretional architecture model mainly refers to the mouth bars which are developed at the margin of breached distributary channel when the hydrodynamic force became stronger. In the study area, there are 129 single mouth bars and 12~24 mouth bars that are developed in the single layers. The single mouth bars are about 500 m long and 450 m wide. The dip angle of accretional architecture mouth bar is 0.31°~2.40°, which decreases from bottom to top. The remaining oil distribution can be divided into 4 patterns, namely retention, one-way effect, poor water injection effect and planar interference patterns. Various development programs and measures can be adopted to enhance oil recovery