［Objective］The aim of this study was to reveal the species composition，community structure，and growth characteristics of herbaceous plants in the understory of mixed plantations in loess hilly areas，and to explore the impact of herbaceous plants on water interception in the understory，in order to provide a theoretical basis for ecological restoration and future forest management in the region. ［Methods］ A combination of field surveys and laboratory analysis was conducted in Wuqi County，Shaanxi Province. A pure Robinia pseudoacacia forest was selected as the control group to investigate the vegetation characteristics of the herbaceous layer and their effects on herbaceous interception under five different mixed plantation models （R. pseudoacacia×Armeniaca sibirica， R. pseudoacacia×Prunus mongolica， R. pseudoacacia×Pinus tabuliformis，R. pseudoacacia ×Hippophae rhamnoides，R. pseudoacacia×Caragana korshinskii）.［Results］1）Compared to pure R. pseudoacacia forest，mixed plantations significantly increased the species richness of understory herbaceous plants. The R. pseudoacacia×P. tabuliformis mixed plantation displayed the highest Margalef richness index. However，mixed plantations reduced the species evenness of understory herbaceous plants，with the R. pseudoacacia×P. tabuliformis mixed plantation showing the lowest Pielou evenness index. Different mixed plantations substantially increased species richness but slightly decreased species evenness. 2） Coverage and leaf area index （LAI） of the herbaceous layer varied significantly among different mixed plantation models. The herbaceous interception capacity of mixed plantations was generally lower than that of pure R. pseudoacacia plantation，with the R. pseudoacacia×P. tabuliformis mixed plantation showing the lowest interception capacity. 3）A significant positive correlation between herbaceous layer coverage and interception capacity was found，indicating that higher coverage provides a more effective rainwater interception function.［Conclusion］ While mixed plantation models improve the species diversity of understory vegetation，they may have a slight negative effect on the soil and water conservation capacity of the herbaceous layer，particularly in terms of rainwater interception by the herbaceous layer. Pure R. pseudoacacia plantations，in contrast，exhibit greater potential for rainwater interception， offering important management insights for the soil and water conservation functions of plantations.