Tamarix sp. is a dominant shrub species used for windbreaks and sand fixation in the desert of Northwest China. The successful establishment of Tamarix sp. seedlings and their growth into mature individuals require their adaptation to various adverse conditions, which is the key to the natural regeneration of the Tamarix population. To clarify the root morphology and biomass allocation characteristics of Tamarix ramosissima Ledeb. seedlings in response to changes of groundwater depths at the Daliyaboyi Oasis in the hinterland of Taklamakan Desert, rooting depth, root dry weigh, specific root length, root surface area, specific root area, number of lateral roots, root/shoot ratio, aboveground and belowground biomass allocation, vertical distribution of root biomass of T. ramosissima seedlings with different basal stem diameter classes were analyzed under groundwater depth of 1.8 m and 3.0 m. The results showed that as the basal stem diameter increased, the rooting depth of T. ramosissima seedlings increased, and the root dry weight and root surface area increased, whereas the root length and specific root area decreased gradually, indicating that the root system of T. ramosissima seedlings tended to develop. As the soil depth increased, the root biomass gradually decreased, and the root biomass was mainly distributed in the 0-40 cm soil layer, accounting for 68.42% of the total root biomass. At the sample site with a groundwater depth of 1.8 m, the root depth of T. ramosissima seedlings ranged from 83.5 to 173.5 cm, the root dry weight and root surface area were higher, the allocation of aboveground biomass increased with an increase in basal diameter, the root-to-shoot ratio was 0.95, and the number of lateral roots, total root length, and average diameter of lateral roots were higher than those at the groundwater depth of 3.0 m. At the sample site with a groundwater depth of 3.0 m, root depth varied from 42 to 192 cm, the specific root length and specific root area were larger, allocation of underground biomass increased with the increase in basal diameter, and the root-to-shoot ratio was 0.35. The number of lateral roots and total root length were relatively small, while the average root length of lateral roots was longer than that at a groundwater depth of 1.8 m, indicating that T. ramosissima seedlings adapted to drought stress through the elongation of lateral roots. The root morphology of T. ramosissima seedlings was affected by groundwater depth in the Daliyaboyi oasis, which reflected its adaptability to arid environments.