Abstract: Abstract: Water and fertilizer are indispensable inputs to crop production in modern agriculture. Drought, water shortage and low efficient utilization of water have posed a great challenge on agricultural production and food security in China. New fertilizers with dual functions of water retention and slow release become significant to enhance the utilization efficiency of water, and thereby to ensure the sustainable development of agriculture. Therefore, previous studies on the new fertilizers have drawn much attention in water and fertilizer technology in recent years. This paper explores the preparation method of a novel water-retaining material that incorporated with nano-SiO2 for the slow-release fertilizer with water retention properties. A P(AA-AM)/SiO2 water-retaining composite was fabricated by in-situ polymerization in aqueous solution using acrylic acid (AA) and acrylamide (AM) as raw materials. A water-retaining slow-release fertilizer was then produced by the double-layer coating process. The mass ratio of acrylic acid (AA) and acrylamide (AM) was set as 3.5:1 to synthesize water-retaining materials. The initiator (potassium persulfate and sodium sulfite), crosslinking agent (N, N-methylenebisacrylamide), plasticizer (glycerol), and nano-SiO2 were added by 1%, 0.04%, 15%, and 2% in monomer mass, respectively. A drum coating process was selected to prepare the water-retaining slow-releasing fertilizer, where the inner coating layer was made of polyurethane, with the mass ratio of coating materials to the inner core of 3%, whereas the outer coating layer was P(AA-AM)/SiO2 water-retaining composite material, with a mass ratio to the core of 27%. Fourier Infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetry (TG) were used to characterize the microstructure, morphology and thermal stability of water-retaining materials. A filtration was selected to determine the water absorption of water-retaining material. Soil culture experiment was used to investigate the capacity of water-retaining and water-holding in the fabricated fertilizer. A water immersion method was utilized to explore nitrogen release properties of fertilizer at the temperature of 25℃. The results showed that the water absorption rates of composite materials with nano-SiO2 in deionized water and 0.9% NaCl aqueous solution were 152% and 87% higher than those of only P(AA-AM) materials, while the thermal stability was also significantly improved. SEM images and FTIR analysis indicated that nanoparticles of SiO2 were evenly dispersed into the P(AA-AM) composites, while the silicon hydroxyl groups on the surface of SiO2 increased the cross-linking density of water-retaining materials. Compared with the slow-release fertilizer without water-retaining layer, the water absorption rate and retention rate of slow-release fertilizer with water-retaining layer (after 25 days of incubation) increased by 25.5% and 47.2%, respectively, indicating the releasing duration of fertilizer was extended from 60 days to 72 days. The preparation method of water-retaining composite material that incorporated with nano-SiO2 and water-retaining slow-release fertilizers can provide excellent properties of water absorption and retaining, as well a high performance of slow release in soil. A mechanism of water-retaining was proposed to clarify the slow release of nutrients in the water-retaining material and water-retaining slow-release fertilizers. The findings can offer new insights into high efficiency fertilizers to enhance the utilization efficiency of water and fertilizers.