In the middle and later stages of chemical flooding in heavy oil reservoirs in Bohai Oilfield, profile inversion is prone to occur. This further leads to issues such as intensified intra-layer contradictions, severe ineffective circulation of oil displacement agents and rapid increase in water cut in some production wells, reducing the effectiveness of increasing oil and decreasing water of oil displacement agents. In order to study the profile reversal law and microscopic oil displacement mechanism of chemical flooding in heterogeneous heavy oil reservoirs, the study first conducted intra-layer "separate injection and separate production" heterogeneous core displacement experiments, clarifying the effect of different chemical flooding systems on enhancing oil recovery and the changes in injection and production profiles. Based on this, microscopic visualization experiments were carried out to clarify the distribution and occurrence status of remaining oil in chemical flooding, and further explore the microscopic oil displacement mechanism of different chemical flooding systems. The results indicate that the increase in oil recovery by different chemical flooding systems is in the following order: functional polymer>"high molecular weight" polymer>viscosity reducer. In the process of chemical flooding in heavy oil reservoirs, the dynamic changes in the injection and production profiles are influenced by both oil-water interfacial tension (IFT) and oil-water flowability ratio. Reducing the cluster-like remaining oil in porous media is a crucial mechanism for EOR of heavy oil chemical flooding. Viscosity reducers can reduce IFT and to some extent reduce cluster remaining oil, but the emulsion is prone to remain in the pores and form isolated-island-like remaining oil. “High molecular weight” polymer can increase the viscosity of water phase and expand swept volume. However, due to the poor effect to reduce the IFT, it is difficult to displace oil in small pores, resulting in a large amount of column-like remaining oil. Functional polymer has the functions of thickening the water phase, retaining and increasing resistance in high-permeability layers, and emulsifying capture and carrying. It can effectively increase the flowability of oil, expand swept volume. After water flooding, the oil recovery can be increased by more than 30%.