Nanofluid flooding is of great significance to reduce the cost of oil development and enhance oil recovery. A series of important results have been achieved about the research on the mechanism of nano-fluid flooding. This paper focuses on the basic research related to the nanofluid flooding mechanism. And the four mechanisms of nanofluid enhanced flooding are summarized based on the different academic opinions and research results. According to this，it is pointed out that under the combined effects of structural separation pressure，rock wetting change and reduced oil-water interfacial tension，the nanofluid exhibits the dual characteristics of“roll-up”and“diffusion”in the process of oil displacement，thus having enhanced oil displacement. Finally，it is pointed out that nanofluids will have a very broad application prospect in the field of enhancing oil recovery，but a lot of research is needed on the effect and influencing factors of nanofluid flooding. In addition，the effective combination of nanofluid flooding and foam flooding is a way to enhance oil recovery.