[Objective] The characteristics of soil water variation of Haloxylon ammodendron grown under plastic film mulch were determined in order to provide technical support for desertification control in the Hexi Corridor. [Methods] Based on the psammophyte Haloxylon ammodendron of Minqin County in Gansu Province, wheat grass squares were set around Haloxylon ammodendron, and treatments of four kinds of high density polyethylene (HDPE) film mulch with different thicknesses and one control treatment without film were arranged. Soil water content was measured and subjected to statistical analysis. [Results] The soil water content of Haloxylon ammodendron was varied with seasonal rainfall. The soil water content above the 40 cm depth fluctuated greatly under the influence of rainfall. The soil water contents of Haloxylon ammodendron with white film, black film, and shed film were greater than the control treatment without film and the farmland film. During the one-year growing period, the soil water storage was always at the highest and the water consumption was the largest. [Conclusion] The white film had the best water retention performance, and could effectively prevent soil water evaporation and improve water storage ability and moisture conservation.