In this study, the extraction process of Hosta ventricosa root polysaccharide (HVRP) was optimized by response surface methodology (RSM), and the protective effect of HVRP on oxidative injury induced by tert-butyl hydroperoxide (t-BHP) in HepG2 cells was explored. Under the optimized conditions: extraction temperature 84 ℃, extraction time 3 h and solid-to-liquid ratio 1:31, the average extraction yield of HVRP was 23.9%, The mass fractions of reducing sugar, protein and uronic acid in HVRP were 11.17%, 0.6% and 12.31%, and HVRP showed absorption peaks characteristic of polysaccharides but no triple-helical conformation. HVRP had strong in vitro antioxidant activity and could significantly reduce the contents of reactive oxygen species (ROS) and malondialdehyde (MDA) and increase the activity of catalase (CAT), superoxide dismutase (SOD), reduced glutathione (GSH) and glutathione peroxidase (GPx) (P < 0.05, P < 0.01). The results of real-time quantitative polymerase chain reaction (qPCR) and Western blot analysis showed that HVRP could promotes the expression of antioxidant enzymes and consequently protect HepG2 cells from t-BHP-induced oxidation damage by regulating the Kelch-like epichlorohydrin-associated protein 1/nuclear factor erythroid 2-related factor 2/antioxidant response element (Keap1/Nrf2/ARE) signaling pathway. This study provides a theoretical basis for clarifying the antioxidant mechanism of HVRP and its application in functional foods.