As most of the heavy oil reservoirs in Shengli Oilfield enter the development stage of medium and high water cut，it is imperative to change the development mode. Microbial enhanced oil recovery（MEOR）technology can specifically tackle the difficulties in the exploitation of hard-to-recover heavy oil reservoirs，such as multiple rounds of thermal recovery，low efficiency of water flooding，deep heavy oil，and sensitive heavy oil reservoirs，through the in-situ action on crude oils and reservoirs by microorganisms and their growth and metabolism. In the past five years，research was conducted on the MEOR technology for hard-to-recover heavy oil reservoirs in Shengli Oilfield，and major mechanisms of MEOR were revealed，including degradation of heavy components by hydrocarbon-philic emulsifying microorganisms to reduce oil viscosity，viscosity increase by biopolysaccharides to regulate oil displacement，biogas production assisted oil displacement，interface modification to reduce flow resistance of oil，and swelling prevention by modified minerals. On this basis，four key technologies were developed，i.e.，quantitative gene analysis of microbial community in heavy oil reservoirs，high-efficiency activation of in-situ hydrocarbon-philic microorganisms for oil displacement，prediction of production performance with microbial characteristics，and changing biological field by injection-production regulation. The research results were applied on site in 15 low-efficiency heavy oil reservoir blocks in Shengli Oilfield，all of which were highly effective in oil production increase and water cut reduction，with enhanced oil recovery（EOR）more than 3%. The successful promotion of MEOR technology in hard-to-recover heavy oil reservoirs confirms its huge application potential in the conversion and development of heavy oil reservoirs. It is a revolutionary technology for the conversion and development of mature oilfields，quality improvement，and efficiency enhancement，showing broad promotion prospects.