In using GIS technology to help make decisions about where trees or grass need to be planted? we can overlay all sorts of data and analyse the overlain results with little manpower and material resources. Furthermore this process can provide us with two kinds of data such as tables and figures. Taking Xianju county of Zhejiang province as an example, the suitable places for returning land to forestland or grassland are selected and formulated on the basis of the obtained knowledge. The difference between this and some previous research before is that this work adopted maps of large scale. In this way, small terrain features are reflected and precision is improved. It can provid reference material for similar work on data analysis and selection of suitable places for returning land to forestland or grassland.