How to effectively and reasonably assess the ecological risk of the natural/semi-natural landscapes under the fast urbanization process is helpful to optimize the urban land use pattern and to reduce and keep away the urban environment venture. So, in this paper, firstly based on the Landsat TM/ETM⁺ data in 1991, 1997, 2000 and 2004 and combining with the geographic information system (GIS) and landscape analysis techniques, the landscape pattern changes in Beijing region from 1991 to 2004 were measured. Then through quantifying the influences from four factors of inner stability, neighborhood stability, external accessibilities and external pressure within every natural/semi-natural landscape cell, a multi-factor evaluating model for the spatial ecological risk of landscape was constructed. And finally using the model the spatial ecological risk level of natural/semi-natural landscapes in Beijing region was assessed in the process of fast urban expansion from 1991 to 2004. The research showed that: (1)With the rapid urbanization process, the primary characteristic of the landscape changes in Beijing region was the persistent increase of factitious building landscape and the substantial decrease of cropland landscape from 1991 to 2004. The proportion of factitious building landscape cells increased from 5.58% in 1991 to 12.72% in 2004, and that of cropland landscape cells decreased from 33.14% in 1991 to 22.19% in 2004, with approximately an average annual reduction rate of 1%. In the meantime, there also was a durative increasing for the woodland landscape. (2)The landscape ecological risk level of the natural/semi-natural landscapes in the study area put up an ascending tendency during 1991 to 2004. For the natural/semi-natural landscapes in mountain regions, the landscape ecological risk level was better than that in plain areas, and the impact of the rapid urbanization process on the landscape ecological risk level of mountain regions was comparatively faint. (3)There also existed some differences among all the natural/semi-natural landscape styles in the study area. The landscape ecological risk level of forest landscape was the lowermost, and the mixed landscape was the topmost, namely the effect of the fast urbanization process to the fixed landscape was most obvious. (4)The newly increased landscape cells of construction land from 1991 to 2004 in Beijing region were primarily from the landscapes of cultivated land and mixed styles, and the total amount from the two landscape styles was more than 95%. Especially to the mixed landscape, the percentage was the highest and exceeded 60%.