After multi-cycle cyclic steam stimulation（CSS），heat interconnections and high heat-consuming channels form between oil wells in heavy oil reservoirs，which results in low thermal efficiency and poor development effect. Since the combined viscosity reduction flooding for chemical water shutoff and profile control is considered as a green and low-carbon replaced method for effective recovery，studying its mechanisms is crucial to guiding on-site projects. Considering the characteristics of the experimental oil reservoir，this paper selects chemical agents to build the combined viscosity reduction flooding system for chemical water shutoff and profile control，and studies the oil displacement mechanism of the system by laboratory experiments. The results show that water shutoff and profile control agents with high viscosity can reduce the oil-water mobility ratio，enhance the production of residual oil in small pores，effectively inhibit viscous fingering，improve the mobility，and adjust the flow field. Absorbed on the surface of crude oil，viscosity reducers can improve the oil phase flow ability and enhance the oil flooding efficiency. Meanwhile，by blocking throats of corresponding size，emulsion droplets help increase the flow resistance of the channeling-path and expand the swept ranges，which can realize viscosity reduction and profile control. There is synergistic effect between water shutoff and profile control agents and viscosity reducers. Water shutoff and profile control agents improve the emulsifying capacity of viscosity reducers and facilitate them to enter the low-permeability area，which improve the production overall reservoirs. Since the remaining oil at the edges and the residual oil could be produced by using water shutoff and profile control agents and viscosity reducers respectively，the remaining oil saturation is significantly reduced.