Abstract: In order to improve the effect of microbial enhanced oil recovery(MEOR), a new activator was designed by introducing a microbial promoting factor. Through adding 0.05% microbial promoting factor RPOS-12 into activator system, bacteria number increased greatly to more than 8.8×10⁸ cells/mL. Two emulsifying bacteria among them increased significantly, the geobacillus increased from 10⁴ cells/mL to 10⁶ cells/mL and the lipopeptide-producing bacteria increased from 10³ cells/mL to 10⁴ cells/mL. The experiment showed that the emulsification index of diesel reached 100%, the rate of oil viscosity reduction was 95.79%, and the oil displacement efficiency was 95.07%. Physical model test showed that the oil recovery rate increased by 17.7% in reservoir conditions. The field test showed that the test single well oil production increased from 4.3 t/d to 8.1 t/d, the water content decreased from 95% to 86.5%, the incremental oil production of the 4 wells was 1 639 t during the new activator injected for 6 months.