This paper proposed a new algorithm to reshape a simple polygon on the basis of its area. Three adjacent vertexes were firstly chosen to form a triangle. The area of the triangle was then compared with a predefined value. Based on the difference between the two values, a new vertex was created to replace an original one. In this way, the polygon could be reshaped and its area could be kept equal to the user defined value. A probability domain was incorporated to limit the searching directions and the users were allowed to select adjusting vertexes in an interactive manner. The “rose” method was also introduced in this study in order to improve the efficiency. This GIS-based approach was successfully applied to the County-level Spatial Data Collection Information System and the Province-level Land Use Planning Management Information System of Zhejiang Province.