Abstract: As urbanization developing rapidly, more and more attentions have been paid to the evolution of urban spatial structure by researchers from western countries and China. Taking the Bayanhaote City in Northwest China as an example, this paper analyzes the characteristics of urban expansion and mechanism of evolution from the viewpoint of urban scale, urban shape and urban structure. As a city in the arid area of Northwest China, Bayanhaote has its own features of the process of urban expansion and the mechanism of evolution. The built-up city of Bayanhaote had grown just in the old district slowly before 1980s; since the “New District” was set up, the city has entered in a fast developing stage. The “New District” extends with high-speed while the old district developing slowly. By and large, the Bayanhaote’s spatial structure evolution is due to the law of “first developing in two flanks of main roads, then inside the construction lots”. The development of urban spatial structure is caused by the comprehensive effects of many factors. The drives of economy, government and society are always mingled in the expansion of urban space and the change of structure. In different stages, the factors that influence the evolution of urban spatial structure are different. Economic development may be the basic factor of the evolution of urban spatial structure, whereas administrative force has also played an important role in it. For Ba-yanhaote, government’s modulation and control could even be the most important factor, while the influence of transportation has not yet become obvious up to now.

Key words: urban evolution, urban spatial structure, dynamic mechanism, Bayanhaote City