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China's rapid population growth has inevitably led to a need for cropland expansion to meet food security challenges. In arid regions such an expansion is restricted by limited water resources, and an increase in productivity per cropland area must be achieved while still limiting water use. However, the response of agroecosystem Water Use Efficiency (WUE a. e.) to alterations in cropland use in Northwest China's Hexi Corridor has not been documented in any great detail. This has limited our understanding of the region's water-carbon interactions and, in particular, how effective cropland management and efficient water utilization protocols might be applied there. The response of the region's WUE a. e. to different potential shifts in cropland was evaluated by drawing on growing season (2003–2020), Gross Primary Productivity (GPP) and actual evapotranspiration (ET c act) data. Over this period net cropland area increased, with 12.3 % of total cropland transferred in, but only 2.5 % of cropland transferred out. The trend in growing season WUE a. e. was greatest in cropland regions transferred in (p < 0.05), and lowest in the cropland transferred out, indicating irrigation and field management in cropland could ensure that WUE a. e. could be maintained at a higher level. Among the different cropland transformation types, the impact of cropland change on WUE a. e. was essentially determined by shifting correlations between GPP and ET c act. This correlation was weakened when the water supply increased, heightening the negative impact of ET c act on WUE a. e. , while weakening the positive impact of GPP on WUE a. e.. There was a tradeoff point for the level of irrigation between improving WUE a. e. and crop yield. Suitable water-saving irrigation is crucial to maintaining a relatively high level of WUE a. e. , yet not decreasing crop yield. Water-saving irrigation in the Shiyang River basin was deemed to have limited potential, whereas in the Shule River and Heihe River basins there remains some potential for such irrigation. The present study's results can potentially inform agricultural water and land management in the region, and provide the basis for efficient water resources utilization. • Agroecosystem Water Use Efficiency (WUE a. e.) was evaluated considering cropland transformations. • The cropland transferred in (∆ CL ←) and out (∆ CL →) in Hexi Corridor was investigated. • The trend in WUE a. e. was the highest in the ∆ CL ← area, and lowest in ∆ CL → area. • The response of WUE a. e. to cropland change was regulated by the correlation of GPP and ET c act. • The correlation of GPP and ET c act is weakened along with an increase of water supply. [ABSTRACT FROM AUTHOR]