The planting scale of Salvia miltiorrhiza continues to expand, producing many stems and leaves, resulting in a huge waste of resources. Drought significantly affects the production and accumulation of active components in medicinal plants. This study used ‘Chuan Danshen 1’ (CDS-1) as the material and used the soil water stress method to study the effects of long-term water stress on the total phenolic acids (TPA), the contents of 8 major phenolic acids and the antioxidant activity of the stem and leaf ethanol extracts. This study preliminarily clarified the response behavior and antioxidant capacity of phenolic acids in S. miltiorrhiza stems and leaves to soil water stress, and provided scientific theoretical guidance for the development and utilization of S. miltiorrhiza stems and leaves. The results showed that: (1) TPA of CDS-1 stems and leaves was sensitive to soil moisture. The TPA content of August, September and October samples (SL-8, SL-9 and SL-10) increased as the soil relative water content (SRWC) decreased, but there are significant differences between different months. Under the same SRWC, SL-9 has the lowest TPA content, only 41.4%-91.1% of SL-8 and 24.0%-79.9% of SL-10. (2) Under long-term soil water stress, the rosmarinic acid, salvianolic acid B, caffeic acid and protocatechuic aldehyde were significantly accumulated in the stems and leaves of CDS-1. Drought stress increases the contents of TPA and single phenolic acid, but severe water shortage (SRWC is 35%) will reduce the content of phenolic acid. (3) Ethanol extracts of the CDS-1 stems and leaves had strong antioxidant activity, and their DPPH· and ABTS·⁺ scavenging activities increased with the decrease of SRWC, which was consistent with the change trend of TPA content. It was found that moderate drought stress significantly increased the phenolic acid content and antioxidant activity of the CDS-1 stems and leaves. Scientific irrigation technology can be used to increase the phenolic acid content of the stems and leaves in the cultivation of S. miltiorrhiza to promote the comprehensive utilization of S. miltiorrhiza.