In high-temperature and high-salinity reservoirs, HPAM is prone to thermal degradation, salt-induced chain shrinkage and shear instability, which weakens its mobility-control ability. In view of the above problems, this paper prepared bifunctional modified nano-SiO₂ (KH570@SiO₂-AMPS/ODMA, DF-SiO₂), and constructed a composite gel system with HPAM. Its performance was evaluated by structural and rheological characterization, aging and shear recovery, and heterogeneous core displacement. At 90 °C and about 20,000 mg/L salinity, the viscosity retention rate exceeded 70% after 90 days of aging, and recovered to 94.6% of the initial value after 72 h of standing following shearing. Core displacement shows that the system can improve the flow distribution of heterogeneous reservoirs, and the recovery of high and low permeability layers is 6.95 and 4.41 percentage points higher than that of HPAM, respectively. DF-SiO₂ constructs a dynamic network through interfacial interaction and hydrophobic association to improve the stability and structural recovery ability of the system, which provides a new idea for the application of high-temperature and high-salinity heterogeneous reservoirs.