Heterogeneity is a significant feature of many mature oilfields after polymer flooding, which presents great challenges for further enhanced oil recovery (EOR). The displacing fluid after polymer flooding should have the dual effects of improving the swept volume and increasing oil displacement efficiency. At present, alkali-surfactant-polymer (ASP) flooding is an important approach for further EOR after polymer flooding in the Daqing Oilfield. Preformed particle gel (PPG) is a new type of chemical agent with a powerful ability to deform and pass through the pore throat. Here, a series of experiments were carried out to investigate the profile control of PPG/ASP mixed solutions in heterogeneous reservoirs. The results show that, with respect to profile adjustment and EOR after polymer flooding, PPG/ASP mixed solutions are better than ASP-only solutions. Regarding PPG/ASP mixed solutions, PPG and hydrolyzed polyacrylamide (HPAM) could block the reservoir preferential fluid flow pathways via their properties of easy deformation and high viscosity in order to achieve the purpose of improving the swept volume; at the same time, Na2CO3 and petroleum sulfonate could reduce oil-water interfacial tension so as to increase oil displacement efficiency. Besides, compared with ASP-only solutions, PPG/ASP mixed solutions have greater resistance and residual resistance coefficients, higher viscosity, and better flow control stability. Oil recovery enhanced by using PPG/ASP mixed solutions after polymer flooding boasts 3.4% more original oil in place (OOIP) when compared to ASP-only solutions, and the consumption of chemical agents is reduced by 15.8%. Furthermore, the proportion and characteristics of microscopic residual oil distribution after different flooding systems were investigated. The results are consistent with the core flooding experiment and confirm that when combined, PPG and ASP have a synergistic effect on profile control after polymer flooding in heterogeneous reservoirs.