When faults in the large scale power systems are triggered by natural disaster, it is necessary to assess the importance of areas which need to be restored for developing restoration strategies. Due to the shortcoming of betweenness indices for the existing evaluation model, the concept of electricity transmission betweenness is proposed, combining what the complex networks have in common and the electrical characteristics of electrical network and considering the betweenness and the maximum transmission capacity of transmission lines. And then, network condensation degree of each area to be restored is calculated. According to the power characteristics of the generators and loads, the node power betweenness is used to correct the network aggregation index, and the priority, as well as importance index, of the area to be restored is obtained, which can be used as a reference for emergency dispatching system of power supplies. Finally, a simulation based on standard IEEE system is implemented to verify the feasibility and applicability of the proposed method.