The line loss calculating method is constructed based on common information model (CIM). Firstly, on the basis of data demand, the relation CIM model is reviewed. Such as topology of equipment, measure data, line data, transformer data and so on. Secondly, the data source of CIM is definite based of distribution system function module. The data exchange mode between different systems in distribution grid is also constructed. Finally, CIM model is extended based on line loss calculated need. The line loss class and other class are constructed. It takes the example for other advanced applications development.