Hyperbranched polysiloxanes with different phenyl content were prepared by hydrolytic polycondensation. The effect of the introduction of phenyl on the solubility of hyperbranched polymers in CO2 was investigated. The cloud point pressure test shows that the introduction of phenyl group has little effect on the solubility of the polymer with hyperbranched structure in CO2. The increase in the content of phenyl in the hyperbranched polymer does not cause a significant increase in the cloud point pressure, which is expected to achieve good solubility and thickening performance as a CO2 thickener. The interactions between hyperbranched polysiloxanes and linear polysiloxanes with CO2 molecules and the interactions between hyperbranched polysiloxanes were calculated and analyzed through molecular simulation, and found that phenyl-containing hyperbranched polysiloxanes possess lower CED and δ, shows a weaker intermolecular polymer interaction, which is beneficial to the dissolution of hyperbranched polysiloxane in CO2.