On the Loess Plateau, dif ferent vegetation types in a forest water shed play an extremely important ecological role in soil and water conservation. By investigating and observing the 6 major forest types in Caij-i achuan watershed, analytical hierarchy is used to evaluate the vertical structure and water conservation capacity of forest types. Results show that the vertical structure of a good stand type is corresponding to strong water conservation. Accordingly, existing stands of Liujiaao water shed are adjusted and the ability of water conservation is greatly increased by 35. 99%. The most significant increase is the soil available water-holding capacity which is increased by 45. 94% .