Polyaspartic acid (PASP), a biodegradable and environmentally friendly material, enhances fertilizer use efficiency through chelating with nutrient ions, improving nutrient retention capacity in soil, and reducing nutrient loss. Modified PASP features lengthened molecular side chains and an increased number of chelating groups, leading to superior performance in agricultural production. Field experiments show that application of fertilizer containing modified PASP significantly increases both yield and economic benefits of the three major staple crops: rice, maize, and wheat. Among them, rice has a yield increase exceeding 12.15% and a net benefit increase of over 255.09 yuan/mu (1 mu = 667 m²); Maize has a 10.40% yield increase under a 20% reduction in fertilizer input; Wheat shows a 16.65% yield increase and a net benefit increase of 222.83 yuan/mu. Future research should focus on applying fertilizers containing modified PASP to diverse crops and at various growth stages to facilitate industrial-scale adoption.