Urban fringe is a special area with interaction of urban and rural areas. The study of relative research shows that the authoritative theory and methods for demarcating urban fringe have not formed yet, but they are developing gradually from mere qualitative analysis into the combination of the qualitative and the quantitative studies. And maintaining the integrity of administrative units was considered. This article tries to break down barriers of administrative units and gives more precise boundaries by extracting the range of the urban fringe of Beijing respectively in 1994, 1999 and 2004, and using the catastrophe-point method with the TM satellite images. At first, the urban land use information is extracted from the TM images of Beijing in 1994, 1999 and 2004, according to which the proportion of urban land use is calculated. And then, this article detects the abrupt changes of the proportion of the urban land use in different directions, and identifies the inner and outer boundaries of the urban fringe in Beijing according to the breakpoints of all directions. Based on the data, this article analyzes the spatial-expansion characteristics including the expanding amount, types, directions, areas and intensity, and explores their driving forces. The results show that: (1) the expanding speed was increasing step by step, the expanding amount and intensity were both greater in the period of 1999-2004 than those in 1994-1999, the main expanding directions were the east and the north, and the main type was sprawling outwards. Those expanding areas are mostly in Chaoyang, Daxing, Tongzhou and Changping districts. (2) The expansion of the urban fringe of Beijing was limited not only by the geographical conditions, but also by the socioeconomic factors, such as economic development, industrial growth, urban infrastructure etc. , and policy factors as well, such as urban planning.