Abstract: Oil reservoirs are typical extreme environments characterized by high temperature, high pressure, high salinity and anaerobic, and the reservoir micro-organisms are important components. Research on reservoir micro-organisms is of great significance to hydrocarbon resource formation, biogeochemical cycling, and the life origins and evolution. Through literature reviews, the authors in this paper described interaction modes and primary functions of micro-organisms in the reservoir, and summarized mechanisms and advancements in the application of reservoir micro-organisms in enhancing oil recovery, bioremediation of oil pollution, and carbon capture, utilization and storage (CCUS), and identified key issues that need to be addressed in the utilization of reservoir micro-organisms. The reservoir micro-organisms have advantages of low-cost and environmentally friendly in oil and gas exploration and development and environment restoration, indicating promising application prospect. This study could provide references and insights for further research and application in this field.