Fall shoot of Citrus(Citrus reticulata Blanco.‘Nichinan No.1’) cultured in hoagland hydroponic solution were used as experimental materials to study effects of different concentration of H₂O₂ treatments on growing state and physiological indexes of relative electric conductivity(REC),contents of malondialdehyde (MDA) and proline as well as activities of catalase(CAT),superoxide dismutase(SOD) and peroxidase(POD) in C.reticulata leaves under 4 ℃ low temperature stress.Meantime optimum H₂O₂ concentration was selected to alleviate chilling injury of C.reticulata and the mechanism of tolerance to cold in C.reticulata with exogenous H₂O₂ treated was also explored.Results showed that the degree of curl and cell membrane damage of leaf gradually increased with the extension of low temperature stress time in all treated groups of C.reticulata.Both 0.2 mmol·L^-1and 1.0 mmol·L^-1concentrations of H₂O₂applied to hydroponic solution could ease C.reticulata leaves curling and wilting caused by low temperature stress,lower the increase of REC and MDA,reduce the accumulation of H₂O₂,and increase the content of osmotic proline and activities of SOD,CAT and POD in C.reticulata leaves.The 1.0 mmol·L^-1 of H₂O₂alleviated chilling stress on C.reticulata damage more significant than that of the concentration of 0.2 mmol·L^-1.The studies confirmed that the symptoms of leaf curl,wither,fall off and cell membrane damage were caused by treatment of 4 ℃ low temperature in autumn shoots leaves of C.reticulata.And the treatment of 1.0 mmol·L^-1H₂O₂could increase the content of proline and activities of SOD,CAT and POD under low temperature stress,and effectively relieve the damage of cell membrane under low temperature in C.reticulata leaves,to enhance its cold resistance.