Pieris Japonica, belonging to the Rhododendron family, is known for its anti-insect and analgesic properties. Despite previous research, the components and antioxidant activity of Pieris Japonica extract remain unclear. This study aims to identify the optimal extraction process for Pieris Japonica, determine its components, and evaluate its antioxidant capacity. An L9 (3⁴) orthogonal method was employed to optimize the Pieris Japonica extraction process, with the polyphenol content serving as the extraction efficiency index. The extracted components were identified by high-performance liquid chromatography-mass spectrometry (HPLC/MS-MS). Antioxidant activity was assessed via the DPPH test, ABTS radical scavenging test, and FRAP reduction ability test. The optimal extraction process involved soaking Pieris Japonica powder in 60% ethanol with a weight-to-volume ratio of 1:20 (g/mL), followed by eight hours of reflux at 50°C. Under these conditions, the total polyphenol content was 11.2 ± 0.6 mg/g. HPLC/MS-MS revealed that flavonoids were the primary components in the Pieris Japonica extract. The FRAP method determined the total antioxidant capacity to be 1.00 ± 0.05 μmol/mL, while the DPPH method showed a radical scavenging rate of 42.21 ± 4.02%, and the ABTS method yielded a 85.74% scavenging rate, indicating a strong antioxidant activity. The primary components of Pieris Japonica extract were flavonoids, and the extracted plant material exhibited potent antioxidant activity.