To address the issues of easy hydrolysis, excessively rapid expansion rate, and inadequate load-bearing capacity in existing polyacrylic-based expandable resins under high-temperature conditions, this study proposes a novel method for preparing a high-temperature-resistant fiber-grafted expandable resin. By incorporating a high-temperature-resistant five-membered heterocyclic structure into the polymer backbone and reinforcing it with grafted modified polyethylene short fibers, the overall performance of the resin was significantly enhanced. Through systematic optimization of key parameters, including the grafting rate, expansion ratio, water retention capacity, and monomer conversion rate, the optimal reaction conditions for fiber modification and resin polymerization were determined. Thermogravimetric analysis, high-temperature aging experiments, and salt resistance tests demonstrated that the modified resin maintains stable expansion performance under high-temperature conditions of 180°C and in saline solutions with certain mineralization levels. In various complex environments, the maximum expansion time of the resin remained stable at 60 minutes, and the compressive modulus of the gel increased by up to 363% at the maximum expansion ratio. The fiber-grafted expandable resin exhibited excellent delayed expansion properties, high-temperature stability, and superior load-bearing strength, indicating broad application potential in oilfield development areas such as high-temperature fracture and vug plugging and deep high-permeability layer profile control.