As an important function of arid and semi-arid ecosystems，water conservation is the foundation for regional economic and social development. Qilian Mountain is located in the arid and semi-arid region of northwest China，at the intersection of the Qinghai-Tibet，Loess and Mongolia-Xinjiang plateaus. It has high species diversity，an obvious vertical band spectrum，and it belongs to a typical “landscape，forest，field，lake and grass” ecosystem. Therefore，studying the water conservation function of the Qilian Mountain ecosystem is of great significance for maintaining regional biodiversity and establishing an ecological security barrier in the west of China. Seven vegetation types（alpine cushion，alpine meadow，subalpine shrubland，dark coniferous forest，mountain shrub grassland，mountain desert grassland，and temperate desert）along an elevational gradient in the Qilian Mountains were investigated. In each of these vegetation types，soil water content，field water holding capacity，soil bulk density and other indicators are used to evaluate the water conservation function of the regional ecosystem. Compared with other ecosystem types，forest ecosystems，especially evergreen dark coniferous forests，had the strongest water conservation capacity，and therefore，concerted efforts should be made to strengthen their protection.