In order to improve the anti-seepage performance of the cover, this paper aims to use super absorbent polymer (SAP) particles to improve the water storage capacity of the soil, and to mix them into the soil to build an SAP composite soil cover, but the law of water movement is still unclear. In this paper, a series of simple evaporation unit tests and soil column model tests were carried out to measure the changes of the pore water pressure and volume water content in SAP composite soil cover at different depths. The results showed that the saturated volume water content of SAP mixed soil formed by mixing 1% SAP particles into the soil increased by 29%, and the absolute value of the slope in the descending section of the soil water characteristic curve increased by 36%, but the air intake value hardly changed. In the process of water loss, the pore water pressure decreased rapidly, while the volume water content decreased slowly, and there was a strong hysteresis effect. The volume water content (water storage) of SAP composite soil cover decreased with the increase of depth. Under the extreme rainfall condition of once-in-a-century in Nanjing, the infiltration amount of SAP was only 12.7 ml, while that of homogeneous sandy soil cover is 2 510 ml, indicating that the anti-seepage performance is good.