Abstract: High internal phase CO₂-in-water emulsions (C/W) were stabilized with cocamidopropyl betaine (CAPB) and nano-SiO₂ particles. The half-life, apparent viscosity, and interfacial tension of the emulsion were measured. The effects of the concentration of nanoparticles, the type of salt ions and the degree of salinity on the stability of the emulsion were investigated. The results indicated that the half life and displacement efficiency of the emulsions constructed by CAPB (w_CAPB=4.00%) were 4.60 h and 70.33%, respectively. The half-life of the emulsions synergistically by nano-SiO₂ (w_\mathrmSiO_2 =0.70%) particles and CAPB (w_CAPB=4.00%) was 21.92 h, and the displacement efficiency was 77.61%. When the mass fraction of Na⁺ was 7.00%, the former could be stable for 4.04 h, while the latter for 15.24 h. When the mass fraction of Ca²⁺ was 0.05%, the former could be stable for 4.37 h, while the latter for 13.20 h. When the salinity was 1×10⁴ mg/L, the latter emulsion could remain stable for 17.88 h, and the displacement efficiency reached 55.98%. In conclusion, CAPB mainly plays a role in the formation of emulsions, while SiO₂ mainly improves the stability of emulsions. The emulsion system stabilized by SiO₂ and CAPB can improve the simulated oil displacement recovery.