Abstract: A comparative study on photosynthetic characteristics between the genetic modified sweet potato transferred with the Cu/Zn SOD and APX genes (TS) and non-GM sweet potato (NS) was carried out with pot experiments. Three controls, namely the favorable soil moisture (75%~80% of field water capacity, FWC), the moderate drought (60%~65% of FWC) and the severe drought (35%~40% of FWC) groups were used. The Result showed that light response curves of the TS and NS had no significant difference under these three soil moisture conditions. The fitting result showed good performance by non-rectangular hyperbolic model. The net photosynthetic rate (Pmax), light saturation point (LSP) and apparent quantum efficiency , dark respiration rate (Rd) of both TS and NS plants decreased significantly under drought conditions and then continually increased. However, the decrease of TS plant was less than NS plant under stress condition and the recovering was quicker. These results indicated that overexpressing antioxidant enzyme genes enhanced sweet potato photosynthetic capacity, adaptability of drought stress and recovery capability. Light compensation point (LCP) of sweet potato increased significantly under drought stress, but the rise in TS plants was less than NS control. These results showed that transgenic genes to sweet potato enhanced its light environmental adaptability