The reconstruction of transmission networks after blackout is thoroughly studied， and a method of network reconfiguration based on discrete particle swarm optimization（DPSO） algorithm is proposed. The network reconfiguration is represented as a nonlinear optimization problem with the importance load restoration accounting for the maximum percentage of the total load restoration as the objective. In solving the objective network， the load priority， the connectivity of the electric network and various operating constraints are considered. The algorithm proposed has the advantages of target-network coding and network-connectivity checking with high computational efficiency. The effectiveness of the algorithm proposed is proved by the numerical results of a couple of IEEE 57-bus system and IEEE 118-bus system.