This study utilizes a microfluidic chip to delve into the microbial flooding process, simulating MEOR and employing in-situ monitoring through microscopic visualization. The on-chip microbial flooding experiments feature a composite microbial community which swiftly reproduces using petroleum hydrocarbons as the sole carbon source, producing biosurfactants, organic acids, and biogas with notable emulsification and viscosity reduction effects on crude oil. In-situ imaging examines oil displacement, residual oil morphology, microbial dynamics, and MEOR mechanisms across displacement processes. Conclusions highlight microbial strains' robust growth and metabolite effects, with the composite community enhancing viscosity reduction by 74.1%. Facilitated by microfluidic technology, mechanistic studies reveal microorganisms' interactions with oil, leading to emulsification and dispersion. Microorganisms primarily utilize petroleum hydrocarbons at the oil/water interface for growth, whilst use dissolved hydrocarbons in the aqueous phase as carbon sources. Microbial transportation in the reservoir during water injection reveals migration patterns across channels and blind ends, underscoring MEOR complexities.