It is the crux of the coordinated planning for the main grid and distributed grid to carry out joint optimization of the 110 kV substation location and the range of power supply. An approach to the coordinated planning of the main grid and distributed grid is proposed based on the GIS and graph theory. First， the basic attributes of substations are analyzed by means of the GIS and graph theory. Then， a new concept of the adjacency relation loop（ARL） of substation service area is presented. Thirdly， the optimum location of a substation is discussed using the ARL to take the needs of the distribution grid development into full consideration while facilitating the adjustment of the supply range of substations available. The definite substation service area and site selection are iteratively optimized to realize coordinated planning of the main grid and distribution grid.