In view of the aggravation of steel corrosion in microbial enhanced oil recovery （MEOR） technology，Bacillus velezensis 4 - 19 was isolated from the produced water of Changqing oilfield. The oil displacement efficiency of the strain and the synergistic mechanism of the strain on the corrosion inhibition of J 55 steel were investigated. The degradation of heavy components was characterized by crude oil viscosity reduction experiment，four-component analysis and meteorological chromatography analysis. The corrosion inhibition behavior was analyzed by weight loss method，electrochemical impedance spectroscopy （EIS） and scanning electron microscopy （SEM） . The protective mechanism of the film was revealed by combining equivalent circuit fitting and X-ray energy spectrum （EDS） . The results showed that 4 - 19 could reduce the surface tension of crude oil by 54 . 5 % and the viscosity of crude oil decreased to some degree，after the action of strain 4 - 19 for 3 days. The content of saturated hydrocarbons in crude oil increased from 49 . 5 % to 58 . 4 %，the content of aromatic hydrocarbons and resins decreased from 17 . 6 % and 27 . 4 % to 14 . 5 % and 22 . 3 %，respectively，and the content of asphaltene decreased from 5 . 5 % to 4 . 8 % . The corrosion rate of the J 55 steel decreased by 75 . 1 % . EIS analysis showed that the film resistance （R_b） increased by 42 . 6 % and the polarization current density decreased by 76 . 7 % . By secreting lipopeptide biosurfactants to degrade heavy components and competitively consume oxygen，4 - 19 formed a dense corrosion product film to realize the coupling of oil displacement and corrosion inhibition function，which provided a new strategy for MEOR field application.