CO2-assisted steam thermal recovery is an efficient CO2-enhanced oil recovery (CO2-EOR) technique, increases heavy oil production while storing CO2. To elucidate heavy oil and supercritical CO2 interactions under high-temperature and high-pressure conditions, PVT experiments were conducted, and molecular dynamics (MD) simulations were used to examine the effects of temperature and pressure on diffusion and dissolution in CO2. The analysis considered oil and gas density distributions, interaction energies between SARA fractions and CO2, radial distribution functions (RDFs), and diffusion coefficients obtained from mean square displacement (MSD). The results show that increasing temperature reduces the dissolved gas–oil ratio but enhances the volume coefficient. Light components such as saturates and aromatics interact most strongly with CO2 and dissolve fastest, whereas heavy components such as resins and asphaltenes have lower interaction energies and dissolve more slowly because of strong π–π association. The interaction energy between CO2 and light components is 2–4 times stronger than that with heavy components in the temperature range 373–523 K and pressure range 5–20 MPa. The CO2–SARA interaction energy decreases by about 30%–40% with increasing temperature, but increases by about 50%–60% with increasing pressure. The diffusion rate of SARA molecules is fastest at 523 K and 20 MPa, with diffusion coefficients of 34.8 × 10−9, 20.4 × 10−9, 6.2 × 10−9, and 4.7 × 10−9 m2/s, respectively. Overall, an injection temperature close to 250 °C combined with pressures exceeding 10 MPa provides optimal conditions for CO2 diffusion and dissolution, thereby facilitating the extraction of light fractions and maximizing viscosity reduction and thermal recovery performance.