The ternary composite flooding technology is one of the important measures for the sustained and stable production of Daqing Oilfield. In order to clarify the changes in residual oil distribution before and after ternary composite flooding in different permeability intervals longitudinally, the adjustment of oil layer profiles after ternary composite flooding, and to study the relationship between reservoir heterogeneity and enhanced oil recovery by ternary composite flooding, it is necessary to use sealed core well data that can most intuitively reflect the distribution characteristics of residual oil. This article adopts mathematical statistical methods, based on the data of two sealed core wells drilled before and after the ternary composite flooding in Block X in the central part of Xingbei Oilfield, combined with the geological characteristics and development process of the development area, qualitative judgment of core oil content observation and quantitative analysis of oil displacement efficiency measured in the laboratory, to clarify the water washing status, oil production conditions, and remaining oil distribution characteristics of the oil layer near the mainstream line between injection and production wells before and after the ternary composite flooding. Analysis shows that the ternary composite flooding effectively adjusts the interlayer and intra layer profiles, increasing the average thickness of production by 4.2%, increasing the proportion of strong water washing by more than 15.3%, and improving the average oil displacement efficiency by more than 6%. From this, it can be seen that, controlled by the improvement of oil displacement efficiency and the influence of layer heterogeneity and interlayer obstruction, the remaining oil distribution after ternary composite flooding is further scattered, making it difficult to tap the potential. The main direction for exploring the remaining oil after ternary composite flooding should be to increase the swept volume. Further releasing the remaining potential of the injection production well network diversion line position and the relatively large permeability gradient within the layer is the main direction of future exploration of remaining oil potential.