In order to further enhance the efficient application of nano oil displacement technology in low-permeability reservoirs，it is urgent to develop a new type of nano oil displacement products. As an environmentally friendly material，Nanostarch particles have a wide distribution in the world with the relatively low price，excellent performance，so that it has the potential to significantly improve oil recovery. In this paper，the process and mechanism of enhanced oil recovery of nano starch fluid were studied based on the basic physical properties of nano fluid，improving oil displacement effect，expanding the swept volume and other key indicators. by using the indoor static experiments，core displacement experiments，microscopic visualization experiments，CT scanning experiments，etc. The experimental results showed that，after the action of the nanostarch fluid with the concentration of 5000 mg/L and the size of 30 nm，the occurrence state of water molecules was changed. The phase transition temperature of water was increased from 102 ℃ to 110 ℃. The wetting contact angle of rock surface was reduced from 78 ° to 34.2 °，the oil-water interfacial tension was decreased from 20 mN/m to 0.56 mN/m，and the injection pressure was decreased by 39.6% . In the microscopic visualization model，nano starch fluid could significantly reduce the oil saturation，especially the amount of oil film on the solid surface of the porous media was significantly reduced，which could significantly improve the oil displacement effect. In low permeability cores，the displacement front of nanostarch solution was more uniform and had a higher sweep area than that of water flooding. Due to its large sweep volume，high oil displacement efficiency and good wettability，the nanostarch fluid could be used to enhance oil recovery in low-permeability porous media. After injection of 0.4 PV of nanostarch fluid with the concentration of 5000 mg/L，oil recovery was increased by up to 21 percentage point. The results of this study can provide a new technical approach for enhanced oil recovery in low permeability reservoirs.