Following a large scale blackout， the failure of switching transmission lines in the process of implementation of certain restoration scheme will seriously delay the restoration process. Based on the relative failure probability of switching transmission line and its result， a risk index for assessing the performance of restoring lines in the network configuration is defined. Analysis is carried out on the three network reconfiguration schemes of IEEE 30-bus system. The results verify that the proposed index can effectively evaluate the risk of restoring transmission lines among different schemes by the crossover particle swarm optimization and the shortest path algorithm. Then the urgent scheme for the failure of certain line restoration is given. It further improves the assessment framework of network reconfiguration schemes.