The SAP (Super absorbent polymer) was synthesized by water solution polymerization. The absorbency rate was above 800g/g and the saturation point was within 50mins. The effect of the amount of the co-monomers and cross-linking agent on water-retention capacity at constant pressure and temperature was investigated. The results showed that the water-retention capacity of the SAP were above 30% after being placed at constant pressure for seven days. The results also show that the water-retention capacity increased at first and then decreased with the increase of the amount of acryl-amide and MBA. At the same time, the water-retention rate of the SAP were above 75.5 % after being placed at constant temperature (50℃) for seven hours, which demonstrated that the SPA can improve the saturated water content of the sand and the water-retention capacity of the sand efficiently and will provide the desert with excellent water-retention agent.