Abstract: Spatial interaction in urban agglomeration is an important driving force of urbanization in contemporary China. Most of the research based on cellular automata has focused on simulating one single city, and does not factually represent the more expansive processes of urban agglomeration. How to quantify the spatial interaction between cities and combine them in a CA model is an issue when simulating the evolutionary processes of urban agglomeration. This paper proposes an urban agglomeration simulation model based on spatial interaction(UASMBSI) that is better suited for simulating the sprawl of urban agglomeration by combining an urban flow model with a CA model. The UASMBSI is applied to simulate the urban sprawl in the Wuhan metropolitan area, with more accurate simulation results than the CA model that does not account for spatial interaction. A case study not only indicated that the spatial interaction plays an important role in simulating the sprawl of urban agglomeration, but also suggestes that the UASMBSI can represent the characteristics and rules for city development, especially the expansion of urban agglomerations.