The fracture structure of the Chang 8 reservoir in the Honghe oilfield is complex，which belongs to a low porosity and ultra-low permeability reservoir. The reservoir heterogeneity is strong and the residual oil saturation is high. Because the water phase permeability is low，and the water injection pressure rises rapidly，which exceeds the fracture restart pressure，resulting in serious water channeling and poor effect of water injection development. Combined with the characteristics of nano and microemulsion，a nano-SiO₂ microemulsion depressurization and injection-augmenting system was designed，and the temperature resistance， interfacial tension reduction ability，solubilization and formation compatibility of the system were systematically evaluated，and the core depressurization and injection-augmenting displacement experiment was carried out. The experimental results demonstrated that the nano-SiO₂ microemulsion system not only exhibited excellent temperature resistance and salt resistance but also possessed high interfacial activity，reducing the oil-water interfacial tension to approximately 10^-2 mN/m. The system showed good oil solubilization performance with a solubilization amount of 6.5 mL/30 mL. Simultaneously，the core pressure reduction and injection increase experiment indicated that after injecting 2 PV of 1% the nano-SiO₂ microemulsion system into the cores with the permeability of 0.4 × 10^-3 μm²， the pressure reduction efficiency exceeded above 28% . The depressurization and injection-augmenting effects of the system were evident，meeting the requirements of the field.