Plant photosynthesis and transpiration are important reference indices for evaluating adaptable ability in adverse habits. In extreme growth environment, the selection of slope position is often becoming the key factor determining the success or failure of reforestation. Valley-type savanna is a unique type of savanna that develops in deep-incised river valleys, such as those of the dry-hot valleys in the Hengduan Mountains, southwest China, and the total area of this type in China is approximately 3.0×10⁶ hm². In the dry-hot valleys of China, the dry-hot valley of Jingsha River is typical, where the environment shows the changes from dry-hot to wet weather in one year, and because of its long dry-hot season, tree species often are difficult to survive and grow well. In this study, based on the consideration that different slope positions have different soil and atmosphere condition in the extreme habitat, the effects of slope position on photosynthesis and transpiration of nine main tree species for vegetation restoration in dry-hot season and wet season of the dry-hot river valleys were analyzed. The trial tree species include nine species, there are Azadirachta indica A.Juss, Leucaena glauca L. Benth., Tephrosia candida DC., Eucalyptus camaldolensia Dehn., Acacia auriculiformis A. Cunn., Melia toosenden Sieb.et Zucc., Dodonaea viscosa L. Jacq., Phyllanthus emblica L. and Jatropha curcas L. These tree species all grow in fields. The results showed that: comparing with upper slope position, lower slope position was in favor of keeping leaf net photosynthetic rate (Pn) a relative high level, but this favorable effect of lower slope position on Pn had obvious difference among different tree species. The effect of slope position on Pn was more obvious in dry-hot season than in wet season, while in wet season the favorable effect of lower slope position on Pn decreased at great extent because the dry-hot stress got relieved. Photosynthesis restriction, induced by raise of slope position, was mainly controlled by non-stomatal factor. Whether in dry-hot season or wet season, lower slope position both promoted transpiration rate (Tr) of the tested tree species, which was accordant with the change of Pn. The change of water use efficiency(WUE) with different slope positions was relatively complicated, the effects were different among different tree species and between the two seasons. It is obvious that the lower slope position benefits the photosynthesis of the tested tree species, and which helps trees to spend the dry-hot season. Because water deficit is one of the main factors that restrict the growth of tree species for vegetation restoration in the dry-hot valley of Jingsha River, and the leaf water potential of trees in lower slope position is more higher than in upper slope position, it can be knowed that the difference of water condition may be the main factor that cause the difference of photosynthesis in different slope positions.