Understanding the driving mechanisms of crop suitability is critical for ensuring global food security, particularly in promoting the sustainable development of alpine agriculture and alpine civilizations. In contrast to climate factors, how anthropogenic adaptation measures affect crop suitability remains largely unknown. This overlooked mechanism may explain why climate-driven model simulations underestimate the upper altitude limit for highland barley compared with observed records. Here, we used two decades of site-based phenological observations on the Tibetan Plateau and biophysical modeling, finding that anthropogenic adaptation measures can expand suitable cropping limits. These measures mainly involve breeding genotypes with lower thermal units, which enhance the adaptability of highland barley phenology to cold climates. Such adaptation mechanisms clarify the conflict between thermal niche model predictions and the observed distribution of highland barley up to an altitude of 5000 m. Considering these mechanisms, we developed an explainable framework to predict the potential habitat of highland barley under current climates. Results showed that anthropogenic adaptation measures expanded the suitable cropping area for highland barley by 27 × 104 km2 and the upper altitude limit for highland barley could reliably increase by approximately 50 m. This observation-based evidence underscores the crucial roles of anthropogenic adaptation measures in expanding suitable cropping limits of crops and highlights its importance for supporting food security and simulating accurate crop suitability.