Molecular dynamics simulations were performed to calculate the solubility parameters of oil molecules (such as straight-chain alkanes, cycloalkanes, and aromatics) and CO2 + cosolvent systems. It was found that the solubility parameter of supercritical carbon dioxide (SC-CO2) increases with the increase of pressure at a fixed temperature, decreases with the increase of temperature at a fixed pressure, and increases linearly with the increase of the SC-CO2 system density. The simulated results showed that the nonbonding van der Waals interaction plays a dominant role in the solubility parameter of the SC-CO2 system. Furthermore, adding a certain amount of cosolvent into the SC-CO2 system can evidently improve the solubility parameters of the system. The simulated solubility parameters showed that the CO2 + 20% ethanol molecules are more effective in extracting light hydrocarbons. When the solubility parameters of CO2 + cosolvent systems are identical to those of alkane, cycloalkane, or aromatic systems, the linear relationship between the pressure and temperature can give the guidance for selecting the cosolvent in the SC-CO2 system in the future. Through the simulation, we concluded that the investigations about the light hydrocarbons and CO2 + cosolvent systems can provide a theoretical model for selecting suitable external conditions for CO2 flooding technology.