Landscape index is an instrument commonly used for quantitative analysis of landscape pattern. However, most of landscape indices are generally focused on simple analysis and description of the geometric features of a landscape patch or pattern, while neglecting information on dynamic changes of landscape pattern. In this paper a new landscape index, i.e., landscape expansion index (LEI), is proposed. In contrast with conventional landscape indices, LEI contains information of the formation processes of landscape pattern, so it can be used to analyze the dynamic changes of two or more temporal phases of landscape pattern, since conventional landscape indices only reflect information for one certain temporal phase of landscape pattern. Landscape expansion index was applied to studies on the urban landscape expansion of Dongguan City, Guangdong, China for the period of 1988-2006, and the results indicate that LEI can perfectly identify the three types of urban expansion, i.e., infilling type, edge-expansion type and outlying type. Additionally, based on an analysis of the LEI changes in the urban expansion processes of Dongguan City, it was found that the rule governing urban expansion of Dongguan City is consistent with the phases theory on urban growth. This study further demonstrates that LEI can be used effectively for a quantitative analysis of the dynamic changes of landscape pattern, and LEI proves to be significant to the studies on landscape pattern and its dynamic changes.