The spatial analysis is an important function or a characteristic of GIS.The article chooses the project of converting farmlands to forestry or grass land in the small watershed on Loess Plateau as an object of studying,aiming at researching new methods for applying GIS spatial analysis into the project.Firstly,a new scheme of converting farmlands into forests or grass adapting to the areas based on GIS spatial analysis and rules of geocodes were made.Secondly,using the functions of GIS spatial analysis including slope analysis,aspect analysis,overlay analysis attributive analysis finished the whole process of planning.Finally,the planning map and area statistis tables about converting farmlands into forests or grass land in the small watershed were obtained.The results show that the method may be used in the course of carrying out the project of converting farmlands into forests or grass on the loess plateau with the characteristics of thesmall watershed.