Provincial border regions is a unique geographical space, the cities in this area have the same or similar natural conditions. However, due to the limitation of administrative jurisdiction, the cities seldom seek cooperation opportunity with the cities in the neighboring province. That weakens the driving force of the cities to the regional economy. Therefore, it is significant to establish the central cities in the border region in order to improve the regional development. On the basis of summing up the indexes of domestic and international division of urban space, the authors establish a competitive power evaluation index system of the nine cities in the border regions of Shaanxi, Gansu, Ningxia, Inner Mongolia, and Shanxi. The principal component analysis is adopted in the research to measure the power of radiation score of nine cities in this region. Also, the authors combine model of Converse P. D to establish Voronoi diagram of the nine cities and work out the division of the spatial radiation range of the nine cities. Furthermore, the authors present the track of the dividing line among the cities so as to make further research on the spatial radiation range of the cities. Constructed by the above evaluation index system, quantitative calculation and analysis, and ultimately by the scope of urban space radiation, the author find that the edge of the same or similar area of urban space has a certain range of radiation. However, the border region in a different geographical location, with regional development policies and social organization of production and living factors such as differences in a way, will have some radiation power through quantitative analysis of these results. Therefore, the environmental factor should be considered as one of the indicators.