In order to solve the problems of complicated preparation processes of common profile-controlling and flooding agents and the addition of organic solvents，the micro/nano-polyacrylamide gel dispersions for profile-controlling and flooding were prepared based on reversible addition fragmentation chain transfer（RAFT）aqueous polymerization. First，water-soluble RAFT agent was synthesized using 2-mercaptopropionic acid，carbon disulfide and α-bromophenylacetic acid as raw materials. Then， the polyacrylamide gel dispersions were prepared in pure water by one-step method with RAFT agent，acrylamide，crosslinker N，N'-methylenebisacrylamide bis-acrylamide and initiator （NH₄）₂S₂O₈. The morphology and size of gel dispersions were characterized. The effects of reactant ratio，polymerization temperature，polymerization time and solid content on the properties of gel dispersions were investigated. The rheological and viscoelastic properties，temperature，salinity and pH responsiveness of gel dispersions were studied. The results showed that the gel dispersions had irregular globular structure and the molecular scale was micro/nano scale. The micron diameter of gel dispersions was 0.92—6.13 μm and the diameter of nanoparticles was 48—87 nm. The characteristic of polyacrylamide gel dispersions was close to the Newton fluid，and its viscoelasticity exhibited the characteristic of viscous fluid，which further confirmed that gel dispersions were formed by small gel unit particles dispersing in aqueous solution. The viscosity of gel dispersions decreased with the increase of temperature and pH value，but the degree of reduction was small， and their viscosity was almost not affected by mineralization. Compared with traditional preparation technology of profile-controlling and flooding agents，the method of preparing gel dispersions in pure water had the characteristics of short time， simplified preparation condition，without organic solvent and small molecular scale of product.