<p>This paper prepared nitrogen-doped carbon quantum dots (NCQDs) by pyrolysis using citric acid and urea as raw materials. The NCQDs were then modified with silane coupling agent KH550 and compounded with sodium α-olefin sulfonate (AOS) to synthesize a novel carbon quantum dot viscosity reducer (NCQD-S). The structure and properties of the materials were characterized by transmission electron microscopy, atomic force microscopy, infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The interfacial activity, wettability regulation, emulsification viscosity reduction, and core flooding performance were systematically evaluated. The results showed that the prepared NCQD-S consisted of quasi-spherical nanoparticles with an average particle size of approximately 2.8 nm, exhibiting good dispersibility, a graphite-like structure, and excellent thermal stability. The viscosity reducer significantly reduced the oil-water interfacial tension, converted oil-wet rock surfaces to hydrophilic states, and effectively improved reservoir wettability. Under conditions of 0.1% mass concentration and a water-to-oil ratio of 7:3, the emulsification degree reached 100%, and the heavy oil viscosity was reduced by more than 90%, with the resulting emulsion exhibiting excellent stability. Core flooding experiments demonstrated that the NCQD-S system cumulatively increased oil recovery by 21.21% over water flooding alone. The carbon quantum dot viscosity reducer developed in this study offers the advantages of environmental friendliness, strong stability, and outstanding viscosity reduction and oil displacement performance, providing a novel nanomaterial and technical approach for efficient viscosity reduction and enhanced oil recovery of heavy oil.</p>