Abstract: A constrained fuzzy cellular automata model was established to simulate the spatial regulation boundary of urban land expansion. In the model, theories of variable weight and fuzzy set, area constraint and spatial constraint were introduced. A case study was taken in Taicang city by using this model. The results show that urban land expand by the means of inner-fill firstly, and then expand outward, and it is a type of compact development. The urban expansion direction accords with requirement of the eleventh five-year planning. We find that this model could be used not only to solve the problems of rational scale of urban land, but also to deal with problems of different factors′ influences on land development and fuzzy decision in spatial location flexibly. So the model could satisfy the current needs of land use planning.