Landscape patterns, processes and functions are the main contents of landscape ecology, and they are interdependent and interacting. Landscape patterns and their dynamics has always been an important scientific issue of landscape ecology. Landscape pattern index is the most widely used method among the existing research methods in landscape patterns, despite its suffering from doubt and its limitations. The majority of the existing landscape pattern indices only explain landscape spatial characteristics in different scales from geometrical characteristics, they all fall into the category of static index, and can not indicate landscape dynamic information. Studies of landscape pattern dynamics are mainly through multi-temporal comparison of landscape pattern indices and variety of dynamic models. Landscape pattern indices can not independently indicate landscape dynamic information yet. So this paper presents a new landscape expansion index (LEI) to indicate landscape dynamic information, this index is based on expansion patch area and weak the impact of patch shape, and this LEI is calculated only with ArcGIS and EXCEL software. The spatial expansion patterns of landscape are divided into adjacent expansion pattern and external expansion pattern based on the spatial relationship between the expansion patch and the original patch. The fundamental difference between the external expansion pattern and the adjacent expansion pattern is the changes of patches area and number. The adjacent expansion pattern increases the area of patches, whereas the external expansion pattern increases the number of patches. LEI's value can be used to accurately identify expansionary patches' spatial expansion patterns, only when A₀ = 0 and the original patch that is adjacent to the expansion patch does not exist, the LEI = 1, and the spatial expansion pattern of patches are external expansion pattern; when the LEI is equal to other values, the spatial expansion pattern is adjacent expanding pattern. Furthermore, this LEI is used to the process of landscape's changing to farmland in Guishui river basin from 1998 to 2009 to verify its applicability. Results show that this index can not only quantitatively indicate spatial expansion size of patches, but can also accurately identify the spatial expansion pattern of patches. Therefore, this paper argues that this landscape expansion index has a prospect for wide application.