Abstract: A review of historical evolution of climate conditions in Northwest China is demonstrated. Based upon rich historical documentary records regarding wasteland reclamations for cultivation, the relationship of sizes and benefits of agricultural development with the conditions of temperature and moisture at that time is indicated. In the west Han Dynasty and the early Tang Dynasty suitable climate provided sufficient heat and moisture for large-scale reclamation of wasteland in the Hexi region, resulting in swiftly booming economy, while economy fell in the target region in late Tang Dynasty and mid-Ming Dynasty mainly because climate got cold. And agricultural development or decline in Tarim Basin from the 1st to the 4th century was caused by change of water source. In historical time, frequent over-reclaiming and subsequent leaving the land alone were responsible for the acceleration of land desertification, there were two cases of Wulanbuhe desert's formation and the high frequency of sandstorm during the warmer 13th century as such adverse consequences caused by above actions.

Key words: Northwest China, historical climate, human opening-up activities, land reclamation/ discarding, histori