Based on the theory of fluvial sandbody architecture, the single beach bar was identified and its architecture was analyzed, then the 3D architecture model was built. The discrepancy of the hydrocarbon distribution was present from the angle of sandbody architecture, and the contradiction of oil and water distribution was resolved. In the single depositional time unit in which the thick sandbodies were widely deposited, independent fluid systems may exist in the overlaying sandbodies due to the lateral migration of the channel. Also, in the single channel, the incomplete connectivity and the discrepancy of oil-bearing grade of different sandbodies were caused by the bounding surfaces between the beach bar and the channel fillings sandbodies. Furthermore, the oil saturation and the oil-water interface had considerable difference between wells even in the single mid-channel bar due to the internal bounding surface of the sandbodies.