Abstract: It needs to process a great deal of gray information in the supermarket location and there is no effective software tool to do so. Thus, often this location decision is made based on the human preference and it is more subjective than objective. A model is presented for the supermarket location problem by combining geographic information system (GIS) with gray system theory such that the gray information can be effectively processed. Based on this model, a decision support system is developed. Besides the effectiveness of the system in locating a supermarket, it is used friendly and easy to use. A case study is presented to show the application and effectiveness of the system.