Low-permeability reservoirs are characterized by low permeability, fine pore throats, and high salinity of formation water. Conventional polyacrylamide (HPAM) oil-displacement agents suffer from severe adsorption and retention, insufficient salt tolerance, temperature resistance, and shear resistance, as well as limited oil displacement efficiency. A hydrophobically modified hyperbranched polyamidoamine-acrylamide copolymer (HB-PAO) was designed and synthesized. The polymer features a three-segment molecular structure of “hyperbranched core-linear arm-hydrophobic terminal” and was prepared via a controlled polymerization process of “in-situ initiation and stepwise grafting”. Characterizations including GPC, FT-IR,¹H-NMR, and SEM confirmed the successful construction of its hyperbranched three-dimensional network topology. Performance tests show that HB-PAO exhibits a dissolution time comparable to that of HPAM, while its comprehensive properties are significantly superior: at a shear rate of 2000 s?1, the viscosity retention rate reaches 69%, which is 1.7 times that of HPAM; it maintains excellent viscosity stability under a high salinity of 10×104 mg/L; after aging at 95 °C for 90 days, the viscosity retention rate is 73.6%, 1.9 times that of HPAM. HB-PAO also shows good interfacial activity: at a concentration of 2000 mg/L, the oil-water interfacial tension is reduced by 51.87% compared with HPAM. Core flooding experiments demonstrate that injecting 0.5 PV of HB-PAO solution into low-permeability cores (10-20mD) increases the final oil recovery by 17.8% compared with water flooding and by 9% compared with HPAM flooding. Field tests further verified that this polymer can effectively adjust the fluid injection profile, increasing the average daily oil production of beneficiary wells by 47.8% and reducing the comprehensive water cut by 19.2%. This polymer has been successfully applied, providing a new high-performance oil displacement material for the efficient development of low-permeability reservoirs.