The research on urban expansion in Yixing city shows that the city's growth is greatly affected by river systems and communicat ion networks (roads and bridges).Since they occupy certain land spaces, modeling of urban expansion can be transformed into analysis of their spatial relationships with the city's growth.Based on distance analysis by using grid GIS, this paper is trying to simulate spatial distribution of Yixing city by firstly calculating spatial distances from each cell to the river system, roads, and the former city zone in the whole region to determine the priority of each cell in expansion, and then filling in the whole region according to each cell's priority in expansion.When the total area of the filled cells is near the real urban area then stop filling in and thus the simulated city distribution would be determined.The case study of Yixing city in China shows that the precision of spatial simulat ion can be as high as 80% as compared with the real city.The precision is expected to be improved by taking into account more factors that might affect town sprawl.