Urbanization is an important topic in modern ecology, there are abundant studies conducted on many aspects of it in the past. However, the effect of city scale on urbanization process and the spatial relationships of urban areas in region received little attention. Based on Landsat TM data, the expanding process of urban areas at different scales in Beijing region was described during 1984-2002.The calculation of the expansion degree of built-up lands in the periods of 1984-1991, 1991-1997,and 1997-2001 respectively, and the contribution ratios and annual contribution ratios of the other six land use types to built-up lands showed that, (1) city scale positively affected on the expansion degree of built-up lands in Beijing region in the past 18 years, and the effect was progressively increasing with the process of urbanization.(2) the spatial position and topographical condition also greatly impacted on the expansion degree of urban areas, the nearer the place to Beijing city (the urban center), and the smoother the urban topography, the more expanding opportunity the urban area. (3) The built-up lands mainly assimilated the surrounding farmlands, grasslands and unused lands, which process had resulted in the rapid concentration and sustaining expansion of urban areas at different scales and in different parts of Beijing region.