This study aimed to optimize the extraction process of pectin, the main component in the peel of Akebia trifoliate (Thunb.) Koidz. var. australis, using the ultrasound-assisted cellulase method (1×105 U•g-1) and to analyze its physicochemical properties and in vitro antioxidant activity. Using the response surface methodology, the optimal extraction process obtained for A. trifoliata (Thunb.) Koidz. var. australis pectin (AP) was as follows: solid-liquid ratio of 1:18.9 (g•mL-1), three extractions, enzyme dosage 0.084 g, ultrasonication temperature 50 ℃, ultrasonication time 55.31 min, and pH value 4.565, resulting in an average AP yield of up to 7.41%. A physicochemical property analysis showed that the pH value of the aqueous solution was 5.8, which was acidic. AP was readily soluble in water at room temperature, and its solubility reached 86.9% after heating to 80 ℃. The total sugar content was 32.54%, and the monosaccharide composition, ranked from highest to lowest, included galacturonic acid (75.53%), rhamnose (1.58%), xylose (1.49%), glucose (0.21%), mannose (0.07%), and fucose (0.05%). Infrared spectroscopy showed characteristic peaks appearing at 1 700 cm-1 (ester group C=O) and 1 650~1 600 cm-1 (carboxyl COO-), suggesting a high degree of esterification. Scanning electron microscopy showed that AP had a porous network structure. Additionally, the scavenging rates of DPPH and ABTS free radicals and reducing ability of Fe3+ showed that AP had strong antioxidant activity. This study provides a theoretical reference for the preparation of AP and offers a technical path and theoretical support for the in-depth utilization of A. trifoliata (Thunb.) Koidz. var. australis resources.