Multiscale analysis of species diversity pattern can provide important information to biodiversity conservation. Additive partition of diversity approach is ideal for multiscale species diversity pattern analysis. The approach is used to analyzing the relative contribution of alpha diversity and beta diversity to gamma diversity of plant species in forest and riparian ecosystem in Beijing. The application in forest ecosystem shows that this approach could give us useful information on the impact of forest plantation on plant diversity pattern at multiscale. The application in riparian ecosystem shows that the additive partition of diversity at multiscale is ideal to indicate the plant community degradation. We argued that additive partition of diversity is an valuable analytical framework for multi-scale analysis of species diversity pattern and is an effective approach for the forming mechanism of species pattern.