A water-absorbent resin was prepared using a corn starch/acrylic acid/N,N'-methylene bisacrylamide ternary blend system through radiation crosslinking with a 10 MeV electron accelerator. The structure and thermal stability of the resin were characterized using infrared spectroscopy and thermogravimetric analysis. The relationships between water or saline water absorbency of absorbent and its particle size, the neutralization degree of acrylic acid, and the absorbed doses were investigated. Additionally, the water absorption capability, water retention rate, and degradation rate of the resin in soil were determined. The results demonstrated that a starch-based crosslinked resin was successfully prepared through electron beam radiation polymerization, exhibiting excellent thermal stability and water absorption properties. When the neutralization degree of acrylic acid was 80% and the absorbed dose was 10 kGy, the water absorbency, saline water absorbency, and soil water absorbency of the resin with a particle size of 150-180 μm were 204.4 g/g, 35.9 g/g, and 45.0 g/g, respectively. The water retention rate of soil with added absorbent resin reached 20.7% after one month, representing an improvement by a factor of 2.5 compared to pure water. The degradation rate of the water-absorbent resin can reached 67.2% after four months, indicating a low environmental impact. This study applied radiation processing technology to the design and development of natural polymer-based functional materials, providing theoretical and practical references for preparing starch-based water-absorbent resins using electron beam irradiation.