Frozen ground is an important component of the cryosphere and one of the most sensitive regions to climate change. The difference of water and heat conditions caused by the change of frozen ground environment is an important factor that triggers the energy exchange， water cycle and carbon cycle of the vegetation ecosystem. Water use efficiency （WUE） is the key to link the relationship between carbon cycle and water cycle in ecosystems， reflecting the adjustment and adaptation strategies of vegetation ecosystems to frozen ground degradation. Based on the gross primary productivity （GPP） and evapotranspiration （ET） products of MODIS， this study estimated and analyzed the spatial variation characteristics of vegetation GPP/ET/WUE in the permafrost and seasonally frozen ground area of the Qilian Mountains from 2000 to 2020， and combined with the self-calibrating Palmer drought severity index （scPDSI） to study the response of WUE in permafrost and seasonally frozen ground area to drought. The results showed that： （1） The average values of WUE， GPP and ET of vegetation in the Qilian Mountains from 2000 to 2020 were 0.56 gC·m-2·mm-1， 307.79 gC·m-2 and 443.02 mm， respectively. The spatial distribution characteristics of the three were high in the southeast and low in the northwest； the value of WUE higher than 0.8 gC·m-2·mm-1 is mainly distributed in seasonally frozen ground area， while lower than 0.4 gC·m-2·mm-1 is mainly distributed in permafrost. （2） In the past 20 years， the vegetation WUE in the Qilian Mountains has generally shown a slow decrease trend， but the monthly change trend is “increase-decrease-increase”. The increase trend of vegetation WUE is the most significant in November and the decrease trend is the most significant in June； WUE change in the study area is mainly determined by seasonally frozen ground area. （3） The spatial distribution characteristics of the correlation between WUE and scPDSI in the Qilian Mountains are affected by the distribution of seasonally frozen ground area and permafrost. The negative correlation between WUE and scPDSI is the most significant in June， the positive correlation between WUE and scPDSI in seasonally frozen ground area is the most significant in March， and the positive correlation between WUE and scPDSI in permafrost is the most significant in November. The difference of temporal and spatial distribution between permafrost and seasonally frozen ground is the direct reason that affects the spatial heterogeneity of WUE. The heterogeneity of temporal and spatial change of WUE is the direct reflection of the water consumption of vegetation change and the adaptation of productivity to ecosystem changes.

Keywords： water use efficiency ; permafrost ; seasonally frozen ground ; self-calibrating Palmer drought severity index ; correlation ; Qilian Mountains