The allocation of fixed transmission cost of interconnected multi-area system is investigated in this paper. The cooperate game model of fixed transmission cost is proposed with solution by nucleolus in disconnected local areas. The interconnected multi-area network is disconnected into many local area networks. The fixed transmission cost is allocated to equivalent bilateral power trades among local areas. Further in one local area, the cost is allocated to load at each bus by using nucleolus. The calculation is simple than nucleolus in the whole interconnected multi-area system. The economic signals provided by the cooperate game model is yet available. The effectiveness of the proposed method is verified by the IEEE 14-bus test system with three local areas.