Rhamnolipid，an anionic biosurfactant produced by microbial metabolism，can effectively enhance the development effect of heavy oil reservoirs during the ultra-high water-cut stage. Compared to conventional chemical surfactants，it not only exhibits comparable interfacial regulation capabilities but also demonstrates significant eco-friendly advantages. The rhamnolipid fermentation broth system holds substantial research value and application potential in petroleum production. However，current studies on its action mechanism and reservoir adaptability remain insufficient，limiting its large-scale application. Three ordinary heavy oil reservoirs were used as the research object in Shengli Oilfield，and microfluidic models were employed to simulate reservoir conditions and conduct micro-displacement experiments on the rhamnolipid fermentation broth system. High-speed microphotography and digital image processing techniques were employed to monitor and quantitatively analyze the oil displacement behavior dynamically. The oil displacement effects in different types of heavy oil reservoirs were comparatively evaluated，and their mechanism of action was deeply analyzed. The results demonstrate that the rhamnolipid fermentation broth system effectively enhances oil recovery in all three ordinary heavy oil reservoirs. Its action mechanisms mainly include interfacial tension（IFT）reduction，emulsification，and wettability alteration，which are quantitatively characterized by the values of oil-water IFT，the average droplet size of emulsified oil，and the magnitude of change in average contact angles，respectively. Emulsification is the key factor determining the displacement efficiency of the fermentation broth system，while IFT reduction ensures the effective mobilization of emulsified oil droplets. The synergistic effect of these two mechanisms significantly enhances oil recovery.