Transgenic and non-transgenic sweet potatoes were used as experimental material under 15% PEG-6000 simulated water stress condition.Response of lipid peroxidation,photosynthetic and antioxidative system during water stress in transgenic sweet potato lines (TS) overexpressing IbOr and non-transgenic line (NT),were studied to explore the physiological mechanism of transferring gene increase the drought stress tolerance of sweet potato.The results showed that:(1) As water stress time extended,chlorophyll,carotenoids,photosynthetic parameters such as:Photosynthetic net rate (P_n),Stomatal conductance (G_s),Intercellular CO₂ concentration (C_i),Transpiration rate (T_r) in TS lines and NT plants decreased obviously,while,transgenic sweet potato lines keep higher level than that of NT plants.(2)O^-·₂ and malondialdehyde (MDA) contents of NT were higher than that of TS under normal condition and water stress.The results indicate that transgenic lines have lower reactive oxygen species (ROS) level and smaller lipid membrane damage than that of NT plants.(3)After 24 h water stress,the activities of SOD and POD enzyme increased,and 48 h later,the enzyme activities reached the maximum,while,which in TS lines is significantly higher than that in NT plants.So we can conclude that overexpression IbOr gene could effectively reduce damage degree of sweet potato under the condition of water stress.The tolerance to water deficit may be achieved mostly by improving the antioxidant ability of sweet potato.