More than 20 years of laboratory experiments and field trials have yielded in-depth understanding of the mechanism and a comprehensive system for the microbial enhanced oil recovery（MEOR）technology in Shengli Oilfield，and the technology has been applied to industrial production. The dominant EOR mechanisms，such as microbial interface tropism，hydrocarbon-philic emulsification，and interface wetting modification have been studied thoroughly and characterized quantitatively，pointing out a direction for the transformation and regulation of bacterial species（groups）. We have established a MEOR system integrating molecular biological analysis of flora structure in reservoirs，activation and regulation of functional bacteria for oil production，and three-dimensional physical simulation of oil displacement. The MEOR field trials develop from single well huff-n-puff to microbial flooding and from the single investigation of exogenous microorganisms to the comprehensive study of both endogenous and exogenous microorganisms. In recent years，the adaptability of this technology in reservoirs has been greatly improved through the combination of MEOR and other EOR technologies. At the moment，it has embarked on transformation from pilot tests to industrial applications. As of December 2019，MEOR was applied to the 10 zones in Shengli Oilfield，with a cumulative oil increase of 30×104 t. Besides the effective MEOR field trials in heavy oil reservoirs of Block Zhan3 which was used to be exploited by conventional water-flooding，the MEOR have been made breakthroughs in a high-temperature and high-salinity heavy oil reservoir of Block Xin68 and a heavy oil reservoir subject to inefficient thermal recovery of Block Cao13. For different types of heavy oil reservoirs，complex huff-n-puff technologies，such as those for microbial compound gas，have been developed，enabling a wider application of microbial single well huff-n-puff technology. As of December 2019，MEOR technology had been applied in more than 400 oil wells with single well huff-n-puff，with a cumulative oil increase of 8×104 t.