An trench profile method was used to study seasonal variation of root ecological characteristics of Shap. seedlings under different irrigation treatments. The results indicated the following: (1) Root morphology: under excellent soil moisture conditions, seedlings developed many horizontal roots and root sprouts to compete for light; but under poor soil moisture, the vertical root system expanded its resource space into deeper soil. Plasticity of root morphology is an important strategy to capture water and adapt to the hyperarid environment. (2) Root/shoot ratio: root/shoot ratio increased with declining soil moisture, and this trend was more obvious later in the growing season. Increase of root/shoot ratio is a strategy for adapting to drought. (3) Growth of root system: The seedlings prefer to develop roots in shallower surface layers with less water availability. The growth depth and vertical growth rate of roots increased with decreased soil moisture. (4) Accumulation of root biomass: biomass and surface area of the root system decreased with increased soil depth, with the roots distributed in an 'inverted pyramid' in vertical section view. The formation of root biomass conformed to a logistic 'slow-quick-slow' growth curve, and total biomass decreased with intensity of soil drought. The findings will provide data useful for effective restoration of and better utilization of water resources in hyperarid regions.