According to the characteristics of cognitive radio networks,an automatic construction algorithm of cognitive radio networks,which combines the fish-swarm algorithm and the minimal independent dominating set algorithm in graph theory,is proposed based on the maximal network lifetime.The algorithm consists of two phases： one is to determine the swarm size and the other is to select the cluster heads.The former phase configures the parameters of cognitive users and determines the scope of the cognitive users affected by primary users with minimal energy cost,and the latter minimizes the energy cost in the communication and maximizes the network lifetime as well as the fairness of cluster head selection.Simulated results show that the proposed algorithm is of an total information complexity of O（n） and a time complexity of O（lg（D＋n）） in the worst case,and that it is prior to the exi-sting MWMIDS（Maximal-Weight Minimal Independent Dominating Set） algorithm.Thus,it can be applied to the design of cognitive-radio routing protocol for the purpose of prolonging the network lifetime.