Abstract: In order to study the effect of low light stress on the root growth of Chamaecrista rotundifolia, the relevant indexes of root physiological metabolism under different light intensities, including the natural light intensity (CK), 50% light intensity (LI 50%), 30% light intensity (LI 30%), 10% light intensity (LI 10%), were measured to explain the mechanism of low light stress. The results showed that the biomass, root-shoot ratio and root activity of Chamaecrista rotundifolia were significantly decreased under the low light stress, and the enzyme activity of Na⁺K⁺-ATP in roots under the levels of LI 30% and LI 10% was significantly decreased. With the deepening of low light stress, the activities of SOD and CAT in roots had a downward trend, and the difference of SOD activity among different treatments was significant. The O₂^- production rate, H₂O₂ content, MDA content and membrane permeability of root system showed a increasing trend. Compared with the CK, the contents of soluble sugar and starch in roots under the treatments of LI 50%, LI 30%, and LI 10% were significantly decreased. The activity of nitrate reductase in roots showed a decreasing trend (significant difference among various treatments), while the activities of protease and ribonuclease in roots showed an increasing trend (extremely significant difference between the treatments of LI 30% and LI 10%). As a result, the nucleic acid content in roots was significantly reduced. In summary, the low light stress could reduce the root activity of Chamaecrista rotundifolia, destroy the root membrane system, reduce the distribution of root carbohydrates, affect the root protein synthesis, accelerate the root senescence, and ultimately affected the root growth.