Anthracnose, caused by Colletotrichum species, is one of the most damaging fungal diseases affecting the cultivation of Polygonatum sibiricum, a traditional Chinese medicinal plant. To investigate the effects of Colletotrichum spaethianum infection on the growth and physiological metabolism of Polygonatum sibiricum, we conducted an experiment by root-irrigation the plants with the pathogen. The results indicated that after root treatment, the leaf margins of the plants were the first to show symptoms, beginning with chlorosis and the formation of yellow-brown lesions. These lesions then expanded, eventually leading to complete desiccation and easy detachment of the leaves. Following pathogen infection, there was a decrease in stomatal conductance, transpiration rate, and intercellular CO ₂ concentration in the leaves, yet the maximum photosynthetic efficiency was observed to increase. After infection, the chlorophyll content in leaves remained relatively stable, while the content of soluble protein decreased. The activity of superoxide dismutase (SOD), peroxidase (POD), and the content of malondialdehyde (MDA) all exhibited an initial increase followed by a decrease. Notably, the activity of SOD changed earlier than that of POD and MDA, suggesting that Polygonatum sibiricum has some capacity to resist Colletotrichum spaethianum. However, the growth indicators of Polygonatum sibiricum plants were largely unaffected by the Colletotrichum spaethianum stress. These findings contribute significantly to the understanding of the physiological changes in Polygonatum sibiricum following infection by Colletotrichum spaethianum and provide insights for disease diagnosis and control measures during Polygonatum sibiricum cultivation.