The study of hydraulic xylem adjustments in response to environmental changes so far mainly concentrate on tree and shrub species, whereas the knowledge on xylem anatomy of main roots and its ecological significance for the perennial forb species, is generally limited to only a few cases. Based on the root anatomical traits of perennial herb species, we analyzed the root growth strategies and water transport efficiency in two comparatively climatic zones on the Loess Plateau of China. The results showed that the perennial herb species in the semi-arid area of the Loess Plateau (with annual rainfall of less than 400 mm) had relatively older age (about 7 years), and higher values of theoretical vessel diameter (about 33 μm), mean vessel area (680 μm²), and mean water transport efficiency (1.56 kg m^-1 MPa^-1 s^-1), but the number of vessel (65) and the fraction of vessel area (6.2%) were relatively lower. In contrast, the perennial herb species in the semi-humid area of the Loess Plateau (with annual rainfall of over than 400 mm) had relatively younger age (about 5 years), and lower values of theoretical lumen diameter (about 27 μm), mean lumen area (550 μm²) and mean water transport efficiency (1.12 kg m^-1 MPa^-1 s^-1), but the number of vessel (85) and the fraction of vessel area (7.5%) were relatively higher. Perennial herb species in the semi-arid area of the Loess Plateau had relatively larger lumen diameter and fewer conduits per unit area, and xylem anatomical adjustments prioritized hydraulic efficiency over safety under drought stress. Perennial herb species in the semi-humid area of the Loess Plateau had relatively smaller lumen diameter and more conduits per unit area, and xylem anatomical adjustments prioritized hydraulic safety over efficiency under drought stress. Additionally, the older herb species in the semi-arid region of the Loess Plateau have comparatively larger vessels and higher water transport efficiency. Older herb species had relatively higher biomass and net primary productivity and consequently had greater consumption of soil water content, so the roots of older herbs had higher hydraulic conduct ability for the adaptation to external drought stress conditions. Furthermore, herb species sampled at sites with higher elevation of the semi-humid region of the Loess Plateau had comparatively larger vessels and higher water transport efficiency. Sample sites at the higher elevation were generally located at the top of mountains with relatively poorer habitat conditions, so the herb species must increase the ability of hydraulic conduct function to cope with the potential negative influence of those adverse environmental conditions.