CO₂injection has become one of the most important methods of enhanced oil recovery in tight reservoirs， but some hydrocarbon gases have more viscosity-reducing and miscibility on oil compared to pure CO₂. Therefore，this article studied the saturation pressure and viscosity changes of oil with CO₂and composite gas （CO₂and C₂H₆） by PVT experiments at high-temperature and high-pressure and revealed the percentage of producing oil with different gases，huff and puff pressures，and rounds by core huff and puff experiments at high-temperature and high-pressure. The results show that the C₂H₆ in the composite gas enhances the gas and liquid miscibility，improves the CO₂ viscosity reduction and dissolution ability， and significantly increases the fluidity of oil. With the increase of C₂H₆mole fraction in the composite gas，the saturation pressure of oil increases by 26.54% from 14.24 MPa to 18.02 MPa， and the viscosity of crude oil decreases from 23.68 mPa·s to 8.76 mPa·s. Under different huff and puff pressures，the oil recoveries of composite gas（CO₂ and C₂H₆） are better than that of pure CO₂，and the increase of recovery near the minimum miscibility pressure is higher than under other huff and puff pressures. The percentage of producing oil by composite gases is higher than that of pure CO₂ in the pores of 0.0001-0.001 μm and 0.01-1 μm.