Abstract: The influence of lithological composition on soil mositure and vegetation in semiarid regions are briefly analyzed. The relationships between lithological composition and vegetation in the Loess Plateau, Northwest China, and in the Yuanmao dry and hot valley, Yunnou, Southwest China, are described in this paper.The loess plateau, where most of land is covered with thick loess deposits up to 300 m, ex-periences temperate semiarid climate with an average anaual temperature, precipitation and e-vaporation of 7. 5C～12. 5C, 400 mm～600 mm, and 1000 mm～l400 mm respectively. There is a good relationship between loess thickness and vegetation in the plateau. Precipitation losses by ground evaporation on loess deposits is considerably high because of its fine texture and high porosity. Steppes are distributed in the thick loess region with deep ground water while forests are distributed in the thin loess region with shallow ground water. Forests are also dis-tributed in the rocky hill region where precipitation infiltrates deeply into the ground because weathering fragmental rocks usually have coarse texture and low porosity. In the northern part of the plateau, the loess hill slope covered with sand deposits are prone to shrubs. The de-scribed relationships between vegetation and ground materials may explain why forestation has succeeded in the rock-thin loess hilly regions failed in the thick loess plateau regions in the loess Plateau.The Yuanmou dry and hot valley experiences subtropical semiarid climate with an average annual temperature, precipitation and evaporation of 21. 9 C , 613. 8 mm and 3 911. 2 mm, re-spectively. Different plants were selected for vegetation rehabilitation experiments on hill slopes underlain by different rocks during the period of 1991～1993. The experiments have successfully demonstrated that the hill slopes underlain by terrace gravel deposits suit dense forests while the slopes underlain by schist shrubs and grasses with a few trees, and the slopes underlain by mud-stone suit shrubs and grasses.

Key words: semiarid climate, lithologica composition, vegetation