As a major new field of unconventional oil and gas exploration and development in the future，low-permeability tight oil and gas reservoir is an important force to replace conventional oil and gas resources and support the oil and gas revolution. The nano-fluid displacement in low permeability tight oil reservoir is effective，however，nanomaterials are easy to block micro-nano pore throat，and it is difficult to solve the problems of agglomeration of nanomaterials in aqueous solution. In this study，acrylamide （AM），2-acrylamide-2-methylpropanesulfonic acid（AMPS）and N-12-（2-crotoxyloxy）n-dodecyl-N，N，N-trimethyl ammonium bromide（MEDDA）were used as substrate monomers by the method of free radical copolymerization induced by aqueous solution， the modified nano-SiO₂/polymer displacement fracturing fluid was synthesized by introducing modified nano-SiO₂. The modified nano-SiO₂ displacement fracturing fluid was analyzed and characterized by infrared spectrum，nuclear magnetic hydrogen spectrum and transmission electron microscopy. Then the oil displacement effect of modified nano-SiO₂/polymer displacement fracturing fluid was studied by combining imbibition displacement experiment with nuclear magnetic resonance technology. The results showed that the optimal dosage of modified nano-SiO₂ in polymer system was 1.5%. By comparing the contact angle of different fluids on the core surface，it was proved that the oil displacement efficiency of modified nano-SiO₂/polymer displacement fracturing fluid was achieved by improving the wettability of the rock surface. Compared with the oil displacement fracturing fluid system without modified nano-SiO₂，the spontaneous imbibition efficiency of modified nano-SiO₂/polymer displacement fracturing fluid system was close to 40%，and the imbibition efficiency was increased by more than 1 times. It could also be clearly seen by NMR image that with the increase of imbibition time，the core crude oil saturation in the displacement fracturing fluid with modified nano-SiO₂/polymer was significantly reduced，and the imbibition rate was accelerated，and the imbibition effect was significant.