Abstract:The research studied the Zamu River basin in Qilian Mountains in the arid region in NW China with the use of the distributed hydrological model SWAT(the Soil and Water Assessment Tool that can simulate soil water sediment and nutrient). This paper discussed hydrological response for different vegetation covers at basin and sub-basin scales. The model was able to represent the hydrological cycle even though some discrepancies were observed, probably due to a lack of sufficient rainfall data.This research investigated seven combined cases: forest-deciduous(FRSD), grassland(SPAS),rang-brush(RNGB),FRSD+SPAS,FRSD+RNGB,SPAS+RNGB,and SPAS+URLD(in short for Residential-Low Density). The hydrological responses vary at various spatial scale as well as at various vegetation combinations. At the basin scales, a single vegetation cover would substantially increase the total evapotranspiration amount and basin storage, decrease the runoff, and cause the temporal variations of sustainable water supply. A combination of various vegetation covers would improve the water budget, moderately decrease the total evapotranspiration, increase runoff, ensure the sustainable water supply and decrease the temporal variation of water in the local region. FRSD would increase the soil water capacity and decrease the change of soil water capacity. SPAS would decrease the soil water capacity due to high density roots. Human activity play a negative role in hydrological response in Qilian Mountain and they can reduce the total evapstranspiration and soil water capacity. At the sub-basin scale, the changes of hydrological responses of different vegetation covers showed the same trend as the altitude changes. With the altitude increasing, the depth of runoff decreased and evapotranspiration increased. At one altitude, a change in vegetation would result in different hydrological responses on different slopes, and a slope of 40 degrees is the inflection point where the hydrological responses would change diversely. Based on these analyses, optimized vegetation covers with the best hydrological responses were obtained. FRSD and FRSD+RNGB have very good hydrological response in different terrain in Qilian Mountains. RNGB and RNGB+SPAS also have good hydrological response between 2601 and 3000 m above sea level. FRSD+SPAS performs the good hydrological response between 3000 and 3800 m above sea level. The cold region is above 3800 m above sea level and it′s best to keep the current vegetation in the region. According to similar studies that compared the hydrological response for different plants and for different land use, we would suggest that Picea crassifolia and Sabina przewlskii are dominant plants for FRSD, Cupular willow, Potentilla fruticosa and Spiraea salicifolia L. are dominant plants for RNGB, and that Kobresia pygmaea is dominant plant for SPAS.