In order to screen out the best microemulsion flooding system, the influence of microemulsion performance on the remaining oil of the pores is selected as an index. Through the core oil⁃displacement test and pores of remaining oil experiment, we have proved the remarkable effect of the microemulsion flooding in enhancing the recovery factor from two aspects, macroscopic and microscopic. The results show that the particle size of the best microemulsion for 8 mL n⁃octane, 8 mL water,4.5 mass fraction of Carboxyl betaine,6 mass fraction of N⁃Butyl alcohol,5 mass fraction of NaCl has smaller particle size distribution, higher viscosity, stronger stability and smaller proportion of residual oil containing pores. To compare with the water flooding, the amplification of microemulsion flooding can achieve 10.8% and the final recovery is up to 49.7%.This result proves that microemulsion can remarkably improve recovery efficiency. The ratio of residual oil to pore decreases with the decrease of pore radius, which indicates that pore radius has a significant effect on remaining oil distribution. Compared with matrix core, the ratio of residual oil pore to fractured core is larger and oil displacement efficiency is relatively low.