An in situ CO2 foams (ISCF) formula is presented to investigate its performance in enhancing oil recovery in homogeneous and heterogeneous formations. Surfactant evaluation, sandpack flooding, and microscopic visualization experiments were carried out to determine the biological surfactant for ISCF formula and confirm the feasibility and mechanism in oil recovery improvement. The results showed that biological surfactant A2 had a good foaming performance even in extremely saline solutions of greater than 2.5 X 10(5) ppm, acid solutions of concentration 20%, and high-temperature environment of 100 degrees C. The ISCF system had a good recovery efficiency in homogeneous and heterogeneous porous media. The SARA test confirmed the generated CO2 by chemical reaction could extract the heavy components which led to about 8% viscosity reduction, the inner pressure distribution indicated that ISCF had a better further blocking ability than conventional foam, the average diversion ratio curves demonstrated that ISCF system had a distinct effect on conformance control even in the presence of crude oil, the 2D micromodel experiment revealed that the generated foam was uniform and could occupy a wider pore space, and the permeability variation of produced liquids analysis presented that the even distribution of acid in homogeneous and heterogeneous formations can also contribute to the blockage removal and oil recovery improvement.