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Research on the effects of grassland degradation on soil water conservation in the Sanjiangyuan region of China is essential as it can provide a scientific basis for evaluating and monitoring water conservation in this important water conservation area.Its regional strategic position is extremely important as 1.2% of the total water in the Yangtze River,40% of the total water in the Yellow River,and 15% of the total water in the Lancang River comes from this area.As a result of climate change and human activity,grassland degradation had been more severe in the Sanjiangyuan region since the 1970s.Rangeland degradation not only impacts vegetation,it can also have great effects on soil physical and chemical properties.Changes to the physical and chemical properties of soil can subsequently affect the efficiency of soil water conservation.The vegetation in this region is dominated by grassland.In grassland ecosystems 99% of water conservation capacity comes from the capacity of soil to retain water.While soil water conservation efficiency is influenced by many factors such as vegetation type,land use and land cover,studies have shown that water yield in this region has decreased year by year and that water conservation capacity has declined sharply.These findings show that further studies exploring the impacts of grassland degradation on the function of soil water conservation are of great significance.Field surveys and experimental analyses were applied to detect vegetation biomass,soil moisture and physical characteristics,and soil water conservation capacity of alpine meadows in different soil types in this area.Results showed that above-ground biomass,under-ground biomass,capillary porosity,total porosity,natural water-holding capacity,maximum water holding capacity,and soil water conservation capacity decreased significantly at severely degraded alpine meadows(P0.05).When an alpine meadow deteriorated from not degraded alpine meadow status to moderately degraded and severely degraded alpine meadows,soil bulk density increased gradually.Soil non-capillary porosity,minimum water-holding capacity and capillary water-holding capacity did not change dramatically.The ranges of soil water conservation capacity at the three degradation stages were 1884.32—1897.44t/hm2,1360.04—1707.79t/hm2 and 1082.38—1550.10t/hm2 respectively.Compared with not degraded alpine meadows with different soil types,soil water conservation capacity was reduced by 9.37%—10.35% at moderately degraded meadows,and by 18.31%—27.82% at severely degraded meadows.Reduced soil water conservation capacity was caused by diminished total porosity and capillary porosity and was also indirectly caused by a reduction of above-ground biomass and under-ground biomass associated with the degradation of the alpine meadows.The contribution of capillary porosity to water conservation should be taken into account when evaluating alpine meadow soil water conservation capacity in the Sanjiangyuan region.The results of the correlation analysis showed that soil water conservation capacity was positively correlated with above-ground biomass and under-ground biomass(P0.05).In addition to promoting the evaluation of water conservation function,our findings can be used to provide guidelines and methods for water conservation function monitoring in the Sanjiangyuan region by remote sensing.