The polyaspartic acid-polyacrylic acid interpenetrating network hydrogel (PASP/PAA IPN) were successfully prepared by solvent-free processes. The preparation process was optimized by orthogonal design. The structure and properties of PASP/PAA IPN hydrogel were characterized by FT-IR, SEM and TG. The water absorption at different temperatures and pH conditions was also investigated. Finally, the prepared hydrogel were used as water retaining agent for pot experiment. The results show that the composition of the interpenetrating network has a significant effect on the stability and water absorption of the hydrogel. Based on the combination of stability and water absorption, the final process was selected to 2 mL of acrylic acid, 1 g of EDGE and 16 mg of MBA. The obtained PASP / PAA IPN hydrogel has a liquid absorption rate of 266 g/g and a saline absorption rate of 63 g/g, and has good thermal properties, pH sensitivity and temperature sensitivity. Pot experiment show that the growth, photosynthetic rate, and chlorophyll content of the PASP/PAA IPN hydrogel were better than those of commercially available PAA water-retaining agents under normal watering or drought stress. The photosynthetic rate was 7.82% (normal watering) and 53.44% (drought stress) higher than PAA water-retaining agent, respectively. The chlorophyll content was 58.33% (normal watering) and 249.7% (drought stress) higher than PAA water-retaining agent, respectively.