In order to clarify the basic properties of the novel C-Si quantum dots and their applicability in low-ultra-low permeability reservoirs，the interfacial properties and compatibility of the C-Si quantum dot oil displacement agent were tested and analyzed. Subsequently，the core imbibition and displacement experiments were carried out to explore the macroscopic imbibition and displacement characteristics of quantum dots. Finally，the oil displacement characteristics of quantum dots were revealed from the microscopic level by means of nuclear magnetic resonance analysis and microscopic model experiments. The results showed that the quantum dot oil-displacement agent had the ability to change the core surface to hydrophilicity，meanwhile，it exhibited strong negative charge，as well as good temperature and salt resistance. When the concentration of the quantum dot oil-displacement agent was 0.5%，the imbibition oil-displacement effect was the best，and the imbibition efficiency reached as high as 48.5%，showing a continuous effect during the core displacement process. The particle size of quantum dots was small，so the Brownian motion of quantum dots was more intense，and the quantum dots easily entered the micro-pores. The imbibition efficiency of the quantum dots in the micro-pores of the core could reach up to 30%. The quantum dots expanded the sweep range of the water phase by weakening the hydrogen-bond association of water molecules，and could effectively activate bypassed residual oil，dead-end and corner residual oil. The research results lay a theoretical foundation for improving the oil recovery of low and ultra-low permeability reservoirs using the quantum dot oil-displacement agent.