Aimed at the development status of aged oilfield in our country，some basic performances of the emulsifier formula systems were evaluated and their oil displacement efficiency was investigated，and the feasibility of the EOR experiment through emulsified oil and their mechanisms were discussed. The experimental results showed that the optimized emulsifier formula system HC-5，containing about 20% amino sulfonate amphoteric surfactant，8% OP seriers nonionic surfactant，0.8% stabilizer，2.5% cosolvent， and water as remainder， had excellent performances of salt tolerance and temperature resistance， and had fine dissolubility in mixed salt aqueous solution with over 120 g/L salinity over the entire range of room temperature to 85℃. The HC-5 could emulsify efficiently the oil in the aqueous solutions with high，middle，and low salinity，and the stability of the formed emulsion was excellent. The type of emulsion formed by HC-5 was dependent on the salinity and the water cut in the bulk system. The critical water content for the transformation from the W/O type to the O/W type emulsion may increase with increasing the salinity in bulk system，for example，the critical water cut in the bulk systems with the salinity of 15350 mg/L，40650 mg/L，and 120670 mg/L，respectively，was of 48%，57%，and 68%，respectively. The laboratory experiment of emulsified oil displacement showed that the increase of injection pressure and the profile control effect could be found obviously in the media with low permeability，and consequently the increase of sweep efficiency factor could enhance the oil recovery. As for the media with higher permeability，the mechanism of profile control from the emulsified effect and the oil-displacement mechanism from the decrease of interfacial tension by surfactant may together influence the enhancement of oil recovery.