The Geobacillus stearothermophilus SL-1（referred to as SL-1）is a hydrocarbonophilic emulsifying bacterium isolated from oil reservoir environment. It has strong emulsifying ability for hydrocarbons，with the suitable growth temperature at 65-70 ℃. The oil displacement mechanism and growth law of SL-1 bacteria in porous media were studied by a microscopic visual model and a core sand-packed model. Results demonstrate that in the high-temperature and high-pressure reservoir environment，the addition of SL-1 bacteria can change the wettability of the pore wall，emulsify film-like oil，and strip blind end oil，compared with single activator system for endogenous bacteria in the blank control group. Besides，residual oil displacement is significantly enhanced after the secondary water flooding. Physical simulations of oil displacement show that the combination of exogenous and endogenous bacteria can enhance oil recovery by up to 13.5%，followed by 8.8% with the only endogenous bacteria and 7.2% with the only exogenous bacteria. The number of microorganisms in the combined system of exogenous and endogenous bacteria is the highest，with the gene copy number of about 109 copies/mL，followed by that in the system with only endogenous bacteria about 107 copies/mL，and then that in the system with only exogenous bacteria about 102 copies/mL. Geobacillus has always been activated to be one of the dominant bacteria in the culture solution during four rounds of injection，and its concentration in the produced fluid is negatively correlated with the residual oil saturation of core. It reveals that the hydrocarbonophilic emulsifying bacteria have an important role in increasing the number of microorganisms and enhancing microbial oil displacement in the reservoir environment.