The microbial oil enhanced recovery technology in Daqing Oilfield has been put into operation since the 1960s.More than 50 years of sustained efforts has witnessed encouraging progress in basic research and field applications. The study found that microorganisms actively migrated to crude oil，adhered to it，or produced surfactant to emulsify it. Besides，it was determined that the alkanes and aromatic hydrocarbons were degraded by experimental strains through oxidation. On the basis of laboratory research，field tests on exogenous microorganisms were carried out in extra-low permeability reservoirs，and 93 wells were subject to microbial huff-n-puff tests. Results demonstrate that the average oil increase per well was 149 t，and the cost of bacteria solution and activators per ton of oil increase was CNY 300. In addition，the microbial flooding tests in extra-low permeability reservoirs proved that the accumulative oil increase in Chaoyanggou Oilfield was 60 000 t，with the enhanced oil recovery of 4.95%，and the cost of bacteria solution and activators per ton of oil increase was CNY 557. In particular，it is clarified that the injection-production system was the main factor affecting the microbial flooding. The microbial community structure of typical reservoirs after water flooding，polymer flooding，and combined flooding in Daqing Oilfield were systematically studied to develop highly effective activators. Endogenous microorganism flooding tests with 1 injector and 4 producers in reservoirs after polymer flooding were carried out in Sanan Oilfield，which enhanced the oil recovery by 3.93%，and the activator cost per ton of oil increase was CNY 643.