Abstract: The phenotypic characteristics of Hedysarum mongolicum at three different ages (55, 28 and 8 years) have been investigated at the edge of Mu Us Desert located in the Jingbian County of Yulin City in the Shaanxi Province. Variations in 17 morphological indexes have been analysed using one-way ANOVA and Principal Component Analysis. The study found that the17 phenotypic characteristics varied with the age of H. mongolicum and that the indexes can be categorized into four principal components. After sorting of the first and second principal components, the three H. mongolicum samples with different ages clearly sorted onto the first principal component as the age increased, and the classification were more significant. Correlation analysis between the 17 index scores and a range of rhizosphere factors (soil total nitrogen, ammonium nitrogen, nitrate nitrogen total phosphorus, available phosphorus, total potassium and organic carbon) indicated that ammonium nitrogen was significantly negatively correlated with first-order root length, weight and second-order root length. First-order root diameter was also significantly negatively correlated with available phosphorus and total potassium.