In the arid regions of Northwest China, regional eco-environment and economic construction are controlled and limited by the rationality of land use structure. Taking Zhangye Prefecture in the Heihe River basin as an example, this paper analyzes the changes in main land use types, including cultivated land, woodland, grassland, lands in desertification and their effect forces. The results show that the land use change is controlled basically by physical conditions, and significantly affected by human activity. The increase in cultivated land is directly related to rising in utilization ratio of water resources, and the increase in population is also one of the main causes for cultivated land augment. The cultivated land decrease is mainly related to land desertification caused by irrational human activity. Although woodland change is also limited by physical conditions, the function of human factor is more important than physical effects. The cause of grassland decrease is overgrazing and irrational human activity. Based on the analyses, a suggestion for the principles guiding rational land use structure in the prefecture is put forward in the paper.