In this study, the optimum extraction parameters of polyphenols from leaves of Boehmeria nivea var. tenacissima were optimized, and the antioxidant activity of polyphenols from ramie leaves was evaluated by using gallic acid as a control. Results of polyphenols extraction experiment showed that the ultrasonic power and ultrasonic time have less effect on the amount of polyphenols extraction, and the influence of three factors on polyphenols extraction was ordered as: ethanol concentration (significantly)＞ extraction temperature ＞ solid-liquid ratio. Finally, the optimized polyphenols extraction process parameters were verified and determined as: 1∶33 (g/mL) of liquid-solid ratio, 40% of ethanol concentration and 42 ℃ of the extraction temperature and the amount of polyphenols extraction could reach at 47.97 mg/g under this conditions. The results of antioxidant activity evaluation showed that polyphenols from leaves of green leaf ramie had good antioxidant effects, and the DPPH free radical scavenging ability [IC50 value (0.15±0.00) g/mL], ABTS free radical scavenging ability [IC₅₀ value (2.28±0.03) g/mL] and oxygen free radical absorbing ability [ORAC value (42.41±0.01) g Trolox equivalent /g polyphenol] were significantly superior to gallic acid.