Abstract: A pot experiment was conducted to clarify the effects of water stress on morphological and photosynthetic characteristics of hybrid giant napier (Pennisetum hydridum). The results showed as follows: there were no obviously changes of Hybrid giant napier under the short-term flooding (6 d), however stems grew a large number of fibrous roots and leaves lost green under long-term flooded (21d). The photosynthetic performance, chlorophyll fluorescence Fv/Fm, Fo, Fm and chlorophyll content decreased significantly in the leave of Hybrid giant napier under flooding. Leaves became yellow under drought condition. Chlorophyll fluorescence Fv/Fm, Fo, Fm and chlorophyll content decreased with the drought degree deepen.