Increasingly drought is changing the structure and function of terrestrial ecosystem and as a consequence of which numerous studies have focused on the responses of plants to drought stress in the dry area. Photosynthetic process is an essential process in plant growth, which is sensitive to environmental change. Many evidences have documented that Minjiang dry valley at the upper reaches of Yangtze River is expanding upward as affected by human activity, environmental changes and their interactions under the global climate change scenarios. The ecotone between dry valley and mountain forest is honored by "the last defense" in slowing or restraining the expansion of dry valley, which is also one of the heavy destroyed areas in the "5.12" Wenchuan earthquake. In order to understand the effects of drought on the plant photosynthesis in the ecotone,(Salix paraqplesia and Hippophae rhamnoides), which are two representative plants, were selected to study leaf morphological characters and the diurnal dynamics of leaf gas exchange under the treatments with different drought stress (control: 80% water field capacity (FC), moderate drought stress: 40% FC, and severe drought stress: 20% FC). The controlled water experiment was arranged in the typical ecotone at Jiashan village of Li county (31°32'N, 103°26'E) in Sichuan Province. Five individuals of S. paraqplesia and four individuals of H. rhamnoides were dead under severe drought stress (20%FC) during the drought stress experiment. Drought stress significantly decreased the leaf number, leaf area, leaf mass, specific leaf area, the content of chlorophyll and carotenoids, net photosynthetic rate (Pn), stomatal conductance (gs) and stomatal limitation value (Ls), which are greatly related to the photosynthetic processes of both S. paraqplesia and H. rhamnoides. However, intercellular CO₂ content (Ci) and intrinsic water use efficiency (WUEi) increased with the increase in drought stress. Leaf gas exchange parameters such as Pn and gs were not increased with the increase of photosynthetic photo flux density and air temperature. The maximum of Pn and gs were observed at 11:00 hrs, and the "midday depression" was also observed in these two species. In addition, compared with S. paraqplesia, H. rhamnoides displayed relative higher leaf area, Pn, gs and WUEi under drought stress treatments, indicating that H. rhamnoides is better adapted to drought environment, while S. paraqplesia is more sensitive to drought stress. The results suggested that the plant at the ecotone might receive strong effects under increasing drought conditions as affected by climate change in the future. Drought significantly decreases the photosynthetic efficiency of S. paraqplesia and H. rhamnoides at the ecotone, and leading to decreased plant growth. However, the responses to drought stress were inconsistent between two thespecies. Compared with S. paraqplesia, H. rhamnoides showed relatively greater adaptation to drought environments with higher leaf area, Pn, gs and WUEi. The results from this study provide information for plant selection and species arrangement in relation to vegetation improvement management in the ecotone between Minjiang dry valley and mountain forest.