Despite extensive research on Eurasian agricultural diffusion, the spatiotemporal dynamics of millet agriculture in Northwest China remain contested due to fragmented datasets. This study integrates plant remains, human isotopes (delta C-13), and organic residues from 358 sites to reconstruct dispersal trajectories through K-means clustering, IDW interpolation, and Kernel Density Estimation. Results reveal four phases of millet agriculture in Northwest China: (1) rapid establishment in the Loess Plateau (7650-5750 cal a BP) with C4-dominated diets (delta C-13 >-13.8 %o); (2) northwestward expansion (5750-4550 cal a BP) marked by tripled site density and millet agriculture altitudinal reach to 2500 m; (3) penetration into Xinjiang (4550-3350 cal a BP) via mountain-oasis corridors, despite wheat's rising prominence in few sites; (4) Late Holocene decline (3350-2200 cal a BP) with mixed C3/C4 diets (delta C-13 =-16.8 %o), reflecting wheat's dominance in arid zones. Crucially, field management innovations (ash fertilization, crop rotation) and mid-Holocene climatic optima (30 % higher precipitation) enabled millet's resilience, contrasting with wheat's reliance on westerly moisture surges. We suggested three dispersal pathways-Hexi-Altai, Tianshan oasis, and Kunlun piedmont-underscoring millet's role in bridging Eurasian agropastoral systems. This multi-proxy framework advances understanding of crop-climate-culture interplay in arid landscapes.