Abstract: In urban development,there is a ciose relationship between the planning and the economy. Urban plannings and decisions have a rich economic internal relation. As long as the plannings combine effectively with economy, the plannings and decisions can affect and confine the whole process of urban development. Threshlod theory and it's applications have become a tool for urban planning,e. g. Threshold Analysis Method. It ushers a new way for the plannings connecting with economy. On the lands in area of urban development,to select the positions of an engineering construction may have several projects, but one of them should be the optimization. The procedure of Threshold Analysis Method of urban develop-ment is described firstly, finally it discusses the optimization to the programs of position finding of engineering by the Fuzzy-grey situation decision.