A method to evaluate the network redundancy based on a recursive decomposition algorithm (RDA) introduced by Li and He in 2002 was employed to calculate the reliability of lifeline networks. A redundancy index proposed by Hoshiya and Yamamoto in 2002 was used to represent the redundancy of networks. RDA is shown to be much more effective, as compared with results of Monte-Carlo simulation. In addition, a limitation of the redundancy index is revealed by case studies.