Abstract: This study aimed to investigate the optimal extraction process for polyphenols from Camellia nitidissima Chi and to analyze the total polyphenol composition and antioxidant activities both in vivo and in vitro post-purification. Camellia nitidissima Chi was the raw material and a response surface methodology based on single factor experiments was designed to screen the optimal extraction parameters including ultrasound power, extraction temperature, ethanol concentration and solid-liquid ratio. The extract was purified using Lx-8 macroporous resin, and five specific polyphenolic monomers were qualitatively and quantitatively analyzed using high-performance liquid chromatography (HPLC). Subsequently, in vivo and in vitro antioxidant experiments were conducted on the extract. The results showed that the optimal conditions were an ultrasonic power of 290 W, an extraction temperature of 35 ℃, an ethanol concentration of 55%, and a material-liquid ratio of 1:30 g/mL. Under these conditions, the yield of polyphenols from Camellia nitidissima Chi was 3.53%, the purity was 63.73%. The content of five polyphenolic monomer compounds, namely gallic acid, chlorogenic acid, epicatechin, rutin, and ellagic acid was 0.47, 11.18, 59.03, 18.34, and 16.41 mg/g, respectively. In addition, the polyphenols extracted from Camellia nitidissima Chi demonstrated a significant ability to boost oxidative damage resistance in C. elegans. This was evidenced by a marked increase in SOD (superoxide dismutase) enzyme activity and a decrease in MDA (malondialdehyde) levels within the C. elegans specimens.