This study proposes a genetic algorithm based method integrating the minimal paths and the recursive sum of disjoint products to find maximal network reliability with optimal transmission line assignment for a stochastic electric power network. In our problem, a set of transmission lines is ready to be assigned to branches of the electric power network. Because each transmission line combined with several physical lines has multiple states, the capacity of the electric power network associated with any transmission line assignment is stochastic. Network reliability is the probability that the network can transmit d units of electric power from an electric power generator (origin) to a specific area (destination). The discussed problem exhibits the features of network reliability and assignment problems, and thus it is non-deterministic polynomial-time hard. A simple electric power network and a real one are adopted to demonstrate the efficiency of the proposed algorithm while comparing with several approaches.