In order to enhance utilization of millet straw and reduce fertilizer loss, a novel multifunctional fertilizer (MS-g-PAA/PDMUA) was developed using straw cellulose and linear polymer (PDMUA) by semi-interpenetrating technology. The structure and morphology characterization of MS-g-PAA/PDMUA were measured by fourier-transform infrared, x-ray diffraction, x-photoelectron spectroscopy and scanning electron microscopy techniques, to provide evidence of semi-IPNs networks and component interactions, and the results show that the product exhibited excellent water absorbency (562.3 g/g) and enhanced the soil infiltration. Cumulative release of N, P was 49.2% and 55.1%, respectively, after 40 days, coming up to the Committee of European Normalization (CEN) standard. The agricultural application of MS-g-PAA/PDMUA showed that it could promote growth indexes of wheat, which could improve wheat yields. Therefore, desirable water retention, slow-release properties, and wheat growth effects highlight the product’s potential for agriculture application.