Abstract: In order to explore whether H₂O₂ could improve the chilling tolerance in naked oat seedlings, three-leaf period ‘Dingyou No.6’ seedlings of sand culture were sprayed with 10 μmol·L^-1 H₂O₂ for 12 h before 8℃/5℃(day/night) low temperature stress, spraying distilled water as the control, and 13 physiological indexes related to cold resistance including superoxide anion(O₂^-·), H₂O₂, malondialdehyde(MDA), superoxide dismutase(SOD), catalase(CAT), peroxidase(POD), ascorbic acid peroxidase(APX), ascorbic acid(AsA), glutathione(GSH), soluble sugar(SS), proline(Pro), soluble protein(SP) and heat stable protein(HSP) in the seedling leaves under low temperature stress for 0, 1, 2, 3, 4 and 5 d as well as the plant height and biomass increments of the seedlings processed for 5 d were determined, respectively. By principal component and subordinate function analyses, the effect of H₂O₂ on the cold resistance was evaluated in naked oat seedlings. Compared with the control, H₂O₂ treatment could significantly enhance the plant height increment and biomass increment of naked oat seedlings under low temperature stress, decrease O₂^-· and MDA contents in leaves during low temperature stress and H₂O₂ content of low temperature stress for 2-5 d, and increase the activities of SOD, CAT, POD, APX and contents of AsA, GSH, SS, Pro, SP and HSP of naked oat seedling leaves. From 13 physiological indexes converted data matrix and principal component analysis, the cumulative variance contribution of four principal factors extracted was 85.6%. By subordinate function analysis, spraying H₂O₂ significantly improved the comprehensive evaluation value of the naked oat seedling leaves under low temperature stress for 0-5 d. Therefore, spraying H₂O₂ can improve the cold resistance of naked oat seedlings by regulating the physiological and biochemical metabolism.