定义了一族双环网络N-family,提出了一种计算非单位步长双环网络平均直径的方法,利用VB6.0和SQL Server2000进行了仿真,发现一些紧优双环网络尽管直径最小,而平均直径并没有达到最小,比一阶紧优甚至二阶紧优的平均直径大,定义了一类双优双环网络,它不仅直径达到下界,而且平均直径在N-family中最小. A family of double-loop N-family is defined. A method to calculate the average diameter of non-unit-step double-loop network is proposed. The simulation results using VB6.0 and SQL Server2000 show that although some of the most compact two-ring networks have the smallest diameter, Without reaching the minimum, larger than the average diameter of the first-order or even second-order compact, a class of doubly optimal bicyclic networks is defined, which not only reaches the lower bound of the diameter but also has the smallest average diameter in the N-family.