Recent studies have demonstrated that many forb species in temperate zones develop growth rings in the roots that represent annual growth increments, which are likely to reflect the variations in growth conditions, life history strategies, and climate response sensitivity of the species. However, there are few studies related to growth rings for herbaceous species in the Loess Plateau of China. Our objective was to analyze herb-chronological data from herbaceous vegetation in the Loess Plateau to determine the annual growth variation and life history strategies of perennial forb species under water shortage conditions. In our research, the main roots of 16 perennial forb species at 13 sample sites in the Loess Plateau were collected. Cross-sections (10-15 μm thick) were produced from the proximal end of sampled roots using a sledge microtome. Annual growth rings in the main roots were identified and measured by differentiating between earlywood and latewood in the secondary xylem. Maximum xylem diameter, an indication of hydraulic conductance efficiency, was also measured under a microscope. The changing trends in annual growth rings and maximum xylem diameters with increasing age were identified. The results indicated that most of the forb species (87.5%, 14 species) in the Loess Plateau showed clearly demarcated growth rings in the root xylem that were most likely annual rings. The age distribution in the whole sample was relatively wide (2-14 years), and the average age of sampled forb species was about seven years. The width of annual growth rings of forb species demonstrated a linearly decreasing trend with increasing age, and this is mainly ascribed to the gradual decline in soil water availability over time. With increasing age, the changing trends in xylem diameter could be roughly classified into three types:The xylem diameter of native forb species (Potentilla spp., Oxytropis racemosa, Cynoglossum divaricatum, etc) tended to increase monotonically over time, which indicated that an increase in water availability was associated with an increase in maximum xylem conductivity; by contrast, the xylem diameter of planted forb species (Medicago sativa, Sophora flavescens, and Glycyrrhiza uralensis) tended to decrease monotonically over time, which is evidence of hydraulic failure that corresponds with a loss of vascular transport capacity to the increasing demand for water resources; additionally, the xylem diameter of Limonium bicolor (distributed from the northwestern part of the Loess Plateau to semi-desert regions) increased at first and later decreased, resulting in a curvilinear growth trajectory over time, which indicated the tradeoff strategy between hydraulic conductance efficiency and safety for forbs under extremely dry conditions. Our results presented substantial evidence of the presence of growth rings in the secondary xylem of main roots in perennial forbs of the Loess Plateau, and analyzed the differentiated life history strategies of those species, and that has scientific value for soil moisture conservation and sustainable vegetation development in semi-arid regions.