One major challenge in agro-meteorological research is to accurately predict the impacts of global climate warming on future agricultural production. So the effects of climate warming over the past decades need to be assessed. We analyzed the effects of climate warming on crop planting, structure and yield in 5 northwestern provinces of China with a focus on Gansu Province, utilizing accumulated temperature (≥ 10°C, AT), accumulated negative temperature (< 0°C, ANT) and crop data collected from 1981 to 2003. The analysis led to the following conclusions: 1) climate warming is the main driving force for the expansion of winter wheat toward the north and the west in China, for the rapid increase in cotton planting acreage, and for the expansion of annually multi-crop areas toward the north in China and higher altitude; 2) Climate warming is the direct cause for early seeding of spring crops, prolonged growth duration for thermophilic crops and shortened growth duration for overwinter crops; 3) Climate warming is largely attributed to the dramatic increase in cotton yield.