<p>Trade connects regions and countries where food is produced and where it is consumed. This leads to virtual water flows (VWF) that move water resources indirectly through food trade. Understanding the patterns and factors that drive these VWFs is essential in a world facing freshwater scarcity. This information can guide the development of food security policies and inform investments in agricultural infrastructure. Here, we investigate the spatiotemporal changes in VWF for grain crops from 1985 to 2020 across three spatial scales in China, and identify the primary drivers of total VWF and crop-specific VWF. At the provincial scale, VWFs embedded in grain trade increased by 82.8%, with net exporters of blue virtual water concentrated mainly in water-scarce Northern China. At the subregional scale, total VWFs grew by 75.5%, with Northeast China contributing most substantially; its net VWF increased tenfold during the study period. At the broader regional scale, net VWFs from Northern to Southern China reached 69.0 Gm³ by 2020, including 37.3 Gm³ of blue water. Production scale emerged as the primary factor driving VWF increase, with the consumption pattern also becoming a significant driver. The contribution of each factor to VWF varied across different crops. The VWF pattern and drivers showed large heterogeneity in regions and crops across China. These findings offer valuable insights for the development of virtual water strategies aimed at achieving water and food security in China.</p>